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I-6 Engines For GMCs that came with the Inline 6 Engines

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  #1  
Old July 22nd, 2014, 04:30 AM
Pops Pops is offline
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Default inline six woes

I have owned my truck for about 3 months. Having thoroughly read the "head gasket" thread, I felt I needed to start a different thread. That is, I couldn't find an answer to my problems.
So, I have a beautifully painted and clean engine and compartment (not show but very impressive). The motor doesn't sound bad and seems to be steady from a visual and sound appearance when standing in front of it. It doesn't hesitate once I get going, though, there is a slight vibration with clutch in and on initial take off. A few problems that I thought I should throw out there that may be explainable.
1.) The truck spays blackened liquid on most start-ups. I had to have the dizzy moved when I first got the truck as it couldn't be timed (vacuum advance was against block). This step helped lessen the carbon on the plugs and I was able to turn the mixture screw in about a quarter turn.
2.) The engine is not smooth if you feel the exhaust - erratic puff during idle.
3.) It burns rich, or incorrectly. Very few people tail-gate. I'm sure its the sulfury, acidic stench. The carb looks to be a re-manufactured Rochester one barrel; it responds well to mixture and idle turns.
4.) It doesn't seem to smoke at all while driving. Not even the condensation look. The only time I see any smoke (whitish blue-gray) is on start up. As I mentioned above, my muffler does seem to be holding water, or?
5.) I haven't ruled out head gasket but I would expect steam from exhaust if that were bad. Or, a milkiness in the oil.
6.) Timing marks on pulley don't match engine sound. The best I can get the engine to operate is when the pulley mark is on top of the pulley.
7.) Lastly, the prev-owner said to error on the side of rich when setting the carb. Not sure this was good advise as the plugs were coal black under his settings.

I don't like the vibration I feel when stopped at light. And I am bugged by exhaust smell. New plugs didn't help. If this sounds like your truck, and/or you know what the problem might be, please, please chime in. Thanks.

Last edited by Pops; July 22nd, 2014 at 04:45 AM. Reason: grammar and missing topic
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Old July 22nd, 2014, 04:43 PM
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Default Re: inline six woes

Quote:
Originally Posted by Pops View Post
I have owned my truck for about 3 months. Having thoroughly read the "head gasket" thread, I felt I needed to start a different thread. That is, I couldn't find an answer to my problems.
So, I have a beautifully painted and clean engine and compartment (not show but very impressive). The motor doesn't sound bad and seems to be steady from a visual and sound appearance when standing in front of it. It doesn't hesitate once I get going, though, there is a slight vibration with clutch in and on initial take off. A few problems that I thought I should throw out there that may be explainable.
1.) The truck spays blackened liquid on most start-ups. I had to have the dizzy moved when I first got the truck as it couldn't be timed (vacuum advance was against block). This step helped lessen the carbon on the plugs and I was able to turn the mixture screw in about a quarter turn.
2.) The engine is not smooth if you feel the exhaust - erratic puff during idle.
3.) It burns rich, or incorrectly. Very few people tail-gate. I'm sure its the sulfury, acidic stench. The carb looks to be a re-manufactured Rochester one barrel; it responds well to mixture and idle turns.
4.) It doesn't seem to smoke at all while driving. Not even the condensation look. The only time I see any smoke (whitish blue-gray) is on start up. As I mentioned above, my muffler does seem to be holding water, or?
5.) I haven't ruled out head gasket but I would expect steam from exhaust if that were bad. Or, a milkiness in the oil.
6.) Timing marks on pulley don't match engine sound. The best I can get the engine to operate is when the pulley mark is on top of the pulley.
7.) Lastly, the prev-owner said to error on the side of rich when setting the carb. Not sure this was good advise as the plugs were coal black under his settings.

I don't like the vibration I feel when stopped at light. And I am bugged by exhaust smell. New plugs didn't help. If this sounds like your truck, and/or you know what the problem might be, please, please chime in. Thanks.
Yeah, sounds like a tuning issue for the most part, do you have a vacuum gauge? You can easily find carb/ignition tuning instruction videos on youtube and probably even some for that engine!
If you can't get it fixed up that way then you want to check through everything for failing parts, the ignition system, plugs & wires, coil function, distributor functions, timing. Watch the engine run in the dark at night and make sure there is no arcing from any plug wires anywhere, then verify that your coil is putting out properly. Make sure each plug fires correctly. double check timing (location of #1) if you have relocated the distributor gear.
The last thing would be gas quality, make sure you have a clean filter and clean fresh gas. some vehicles have gas tank condensation problems due environmental factors, use some methyl hydrate(gas line antifreeze) in the tank if needed. Water/condensation in your fuel can cause what you describe here.
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Old July 22nd, 2014, 07:16 PM
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Default Re: inline six woes

Thanks for taking time out to respond. To make sure I don't send advisers off on a goose chase, there are a couple more things worth mentioning:
1. I have a Petronix insert in distrib-- I know nothing about this product
2. I'm not sure how to test coil function. The friend who re-positioned the dizzy couldn't get #1 plug wire to spark off block. He didn't say why. Just said it should have.
3. All newer ignition parts on car; also gas tank, filters, etc. I have timed engine with light, and by ear. Still can't address smell, watery start-ups, or vibration at low RPM's while sitting at light. (and timing mark seems off when using light)
4. The truck came with a power brake booster add-on. Looks like it was meant for the truck - not custom. Do these create vacuum problems if not performing perfectly?
5. It sounds contradictory, but can turning the mixture screw more in counterclockwise direction actually address vibration. It would seem I was going backwards if i make it
more rich.

If I've thrown too much out there, please accept my apology. For now, could you please address coil function, and booster question. The PO had plugged off the vacuum line to booster saying he preferred the feeling of original non-power brakes. I changed booster grommet and put on new hose. I prefer power brakes by far. But, I am now a little suspect about why he really disabled the booster. I'm not throwing any stones right now, but I thought I'd share the last point so I'm not tearing up and replacing things when its in the vacuum system (at booster).
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Old July 23rd, 2014, 07:14 AM
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Default Re: inline six woes

Quote:
Originally Posted by Pops View Post
Thanks for taking time out to respond. To make sure I don't send advisers off on a goose chase, there are a couple more things worth mentioning:
1. I have a Petronix insert in distrib-- I know nothing about this product
2. I'm not sure how to test coil function. The friend who re-positioned the dizzy couldn't get #1 plug wire to spark off block. He didn't say why. Just said it should have.
3. All newer ignition parts on car; also gas tank, filters, etc. I have timed engine with light, and by ear. Still can't address smell, watery start-ups, or vibration at low RPM's while sitting at light. (and timing mark seems off when using light)
4. The truck came with a power brake booster add-on. Looks like it was meant for the truck - not custom. Do these create vacuum problems if not performing perfectly?
5. It sounds contradictory, but can turning the mixture screw more in counterclockwise direction actually address vibration. It would seem I was going backwards if i make it
more rich.

If I've thrown too much out there, please accept my apology. For now, could you please address coil function, and booster question. The PO had plugged off the vacuum line to booster saying he preferred the feeling of original non-power brakes. I changed booster grommet and put on new hose. I prefer power brakes by far. But, I am now a little suspect about why he really disabled the booster. I'm not throwing any stones right now, but I thought I'd share the last point so I'm not tearing up and replacing things when its in the vacuum system (at booster).
I assume that dizzy means distributor and if you cant get #1 wire to spark then your vibration is coming from an engine mis-fire meaning that any wire that is not sparking properly is causing a that cylinder to "NOT FIRE", this will make the engine seem to vibrate or run rough!!!

If the timing mark does not seem to line up properly that is because it is not lining up properly due to the distributor rotor not lining up with your plug wire connections at the distributor.

Don't worry about the water coming out of the muffler or tail pipe it's just condensation.

I assume the petronix is an electronic ignition and it's my guess that this is ok or the engine would likely not be running at all.

You need to properly time the engine by hand. Get valve cover off pull out the number one plug and bring the engine to top dead center. Make sure the valves for number one are closed with a long lag time between valve movement(not the short lag time). Use a long thin screw driver in the plug hole or coat hanger to feel when the piston is positively at the top. Your timing mark should be at "0" now! If you have the piston and valves in the correct position then the rotor in your distributor should be lined up almost right at the #1 plug wire in the cap.

From what you have said I believe that it will not be close to #1. You should pull the distributor and get it lined up correctly or move your plug wires on the cap, keeping them in the correct order, to make them line up properly. You must still have enough swing room to move the distributor for timing adjustments.

If you want to do a poor man's test on the distributor/coil/plugwires then all you do is pull the plug wires off the plugs one at a time and put screwdriver into the plug wire while holding it with a glove on your hand. Bring the screw driver very close to any metal on the engine while running, or your friend turns the engine over and watch for a very bright spark(not a dull one), this is easier if it is a little dark out. If they all spark then all cylinders will fire and the engine should run smooth if your timing is correct. If one of them does not fire then you likely have a bad plug wire unless there is something going wrong with your petronix. If all seems to be ok after all this then start the engine and set your timing like usual, make double sure you put the plug wires in the correct firing order. If there is bright spark then you likely have a good coil.

I still recommend going to youtube to watch videos of using a vacuum gauge for tuning your carb, you will learn the most watching the video. disconnect and plug your brake booster vac line when doing this. you have to make sure there is nowhere to loose vacuum.

The bad smell is just un-burned fuel coming from the engine misfiring, that will go away when this issue is corrected. Making the carb run more rich will make that smell worse because there will just be more un-burned fuel.

Hope this gets you some good results

Last edited by quest; July 23rd, 2014 at 07:25 AM. Reason: mistakes
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  #5  
Old July 23rd, 2014, 01:31 PM
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Default Re: inline six woes

Quote:
Originally Posted by Pops View Post
Thanks for taking time out to respond. To make sure I don't send advisers off on a goose chase, there are a couple more things worth mentioning:

2. I'm not sure how to test coil function. The friend who re-positioned the dizzy couldn't get #1 plug wire to spark off block. He didn't say why. Just said it should have.

4. The truck came with a power brake booster add-on. Looks like it was meant for the truck - not custom. Do these create vacuum problems if not performing perfectly?

5. It sounds contradictory, but can turning the mixture screw more in counterclockwise direction actually address vibration. It would seem I was going backwards if i make it
more rich.

If I've thrown too much out there, please accept my apology. For now, could you please address coil function, and booster question. The PO had plugged off the vacuum line to booster saying he preferred the feeling of original non-power brakes. I changed booster grommet and put on new hose. I prefer power brakes by far. But, I am now a little suspect about why he really disabled the booster. I'm not throwing any stones right now, but I thought I'd share the last point so I'm not tearing up and replacing things when its in the vacuum system (at booster).

#2 Make sure spark is available at the plug from the wire. If not, the resulting skip will cause the problems you are having. (make sure the plug is good too)

#4 An internally leaking booster will cause enough of a vacuum leak to cause your idle quality problem. Leaks in the line/connections from the engine to the booster will do the same. To test, disconnect and plug at the engine connection first, then work toward the booster.

#5 Turning the idle mixture screw further counterclockwise MAY compensate for a vacuum leak depending on the leaks location and severity, provided the carburetor idle system has enough capacity to compensate.
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  #6  
Old July 25th, 2014, 04:20 AM
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Smile Re: inline six woes

Thanks a ton for advice. You guys are great!
So what I did today was set timing and mixture with vacuum gauge. Too easy, but, I felt it may be a more honest setting than using pulley mark. More than one person has said the pulleys wear on rotation components - giving incorrect reading. Made sense. Setting timing at max vacuum (with a little adjustment to steady vacuum needle) actually started the process of resetting everything. It lowered engine rev, vacuum called for leaner setting at carb, I set idle to 550. Today, I feel, improvements were evident. I'm not sure how to tell what the exhaust should sound like but it seems a little more balanced and a little cooler (rapbapbap). lol ..........Smell is still not great. Unburned gasses???

For other readers, I made a stethascope and aimed at all vacuum connections (booster, intake manifold, pcv, around carb, etc. All seemed good. I sprayed carb cleaner at intake gasket and idle did not change. Unless internal issue, I feel pretty sure I've done what I can from outside the engine.

It's a bitter sweet find, but I think the vibration is caused by u-joint problem.

Back to tuning, please share insight if you believe more is needed.
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Old July 25th, 2014, 04:58 AM
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Default Re: inline six woes

Hi Pops, you said the vibration was occurring while stopped at a light? That couldn't be a U-joint as they would vibrate while moving. If I misunderstood, I apologize. A constant "poofing" out the tailpipe can be caused by a weak exhaust valve or seat. I am working on my '72 GMC and it had decent compression on #6 cylinder--125 psi(V-8) but was oil fouling plugs. I pulled a valve cover and ran it up to TDC on #6 to do a leak down and that valve was sitting an 1/8th inch higher than the intake. Valve seat was gone, but the valve was tuff enuff to kinda pound it's own seat into the head casting.

What Rochester one barrel do you have and what engine for that matter? There can be an issue with the power valve needle retainer spring if it is installed on the wrong side of the power piston arm with the Model M "MonoJet" carb. Drawings in the kits can be unclear and assume it was correctly built when they say to reassemble in reverse of dissassembly. I put the spring in the same position as it was installed on mine and it was running rich rough and smelly. Found out that a previous rebuild had put the spring on the bottom of the arm and I just assembled it as it came apart. Put the spring on top and it ran great.

I put a Pertronix in my 230 I-6 in 2011 and have not had any regrets.

DAC
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Old July 25th, 2014, 05:44 PM
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Default Re: inline six woes

Thanks Doug!
Your input is valued. As much evil as we find on the internet, its also an amazingly wonderful asset. I have gotten more information through guys like yourself than anyone else. Never need to apologize. I am still learning what to call things, and, sometimes I don't explain myself well enough.
I have two vibrations going on:
--One is sitting at light and engine is not silky smooth and therefore I feel and hear vibration transfer through cab. My mirror shimmies until I give it a little gas. This is part of the tuning I have been working on. Might add, its more of a vibration than rough running. (May easily be part of valve problem your are referring to.) To be honest, somedays the truck seems to run and smell a little differently. I sometimes want to blame my concerns on a watered down batch of gas, and/or the personality of the Rocheseter. I've also had times where a slightly richer setting helps with vibration.

--The second vibration feels like wheels out of balance between 10 and 35 mph. Whether going up in speed or coming down in speed. It just started doing this in the last month. My first inclination was tie rod components or ball joints as they are older and have deteriorated grease cups. It could be tire belts? But, yesterday I felt a clunk in rear on take off. This just started. Man at parts store said he would bet on u-joints.

Regarding the carburetor, I have a Model B if pictures tell the difference. I don't have a tag (remanufactured) but it does say BC on back side. I believe the "C" represents auto choke though mine is manual. I'm going to check fuel pressure soon as I have read that too much pressure will cause flooding; even leaking. My gasket at float bowl is always moist.

Better stop here or this will become a book - lol.
Have a great day.
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Old July 26th, 2014, 01:23 AM
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Default Re: inline six woes

Quote:
Originally Posted by Pops View Post
Thanks Doug!
Your input is valued. As much evil as we find on the internet, its also an amazingly wonderful asset. I have gotten more information through guys like yourself than anyone else. Never need to apologize. I am still learning what to call things, and, sometimes I don't explain myself well enough.
I have two vibrations going on:
--One is sitting at light and engine is not silky smooth and therefore I feel and hear vibration transfer through cab. My mirror shimmies until I give it a little gas. This is part of the tuning I have been working on. Might add, its more of a vibration than rough running. (May easily be part of valve problem your are referring to.) To be honest, somedays the truck seems to run and smell a little differently. I sometimes want to blame my concerns on a watered down batch of gas, and/or the personality of the Rocheseter. I've also had times where a slightly richer setting helps with vibration.

--The second vibration feels like wheels out of balance between 10 and 35 mph. Whether going up in speed or coming down in speed. It just started doing this in the last month. My first inclination was tie rod components or ball joints as they are older and have deteriorated grease cups. It could be tire belts? But, yesterday I felt a clunk in rear on take off. This just started. Man at parts store said he would bet on u-joints.

Regarding the carburetor, I have a Model B if pictures tell the difference. I don't have a tag (remanufactured) but it does say BC on back side. I believe the "C" represents auto choke though mine is manual. I'm going to check fuel pressure soon as I have read that too much pressure will cause flooding; even leaking. My gasket at float bowl is always moist.

Better stop here or this will become a book - lol.
Have a great day.
I also appreciate the help and education I get on this forum from the experienced folks posting here and hope to pay a little back now and then with some small things I have ran across trying to keep old beaters running on the cheap!-LOL!

Low volume flooding can cause exactly what you are describing, Pops. At idle small amounts of extra fuel will cause the rough idle but soon as more gas is required it will smooth out. The top bowl gasket will stay damp while idling quite often but may actually dry out off idle. The damp gasket is because the fuel bowl is too full possibly from a high float level or a damaged or worn out needle or seat or a float that doesn't float well anymore. If you have the mechanical fuel pump I really doubt it is over pressuring the needle, seat and pressure from the float unless there are the above described damage or wear.
There could also be debris stuck in the seat holding the needle open.
You probably know that the Model B is a dual float carb. They are great carbs and will last forever. I've got a couple and the only reason I went with the Model M is to get the "kick down" type manual choke. my B's require a throttle cable to keep the idle fast while opening the choke. I drive my '55 in pretty cold weather and like the high idle no choke warmup.

The clunk you described definitely sounds like a u-joint, and a bad one can cause vibrations at different speeds and load conditions.

Your carb may be one of these.

DAC
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Old July 26th, 2014, 01:54 AM
Pops Pops is offline
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Default Re: inline six woes

Yes Doug. I have the carb on the right. The fuel inlet is positioned high ;same side as mixture screw. I did remove the upper part of the carb to look at float. I removed float to check drop. Ok on that. I looked closely at float fit ; ok on that too. I did not go deeper into carb for I didnt have any backup parts or gaskets.
the carb looks newly rebuilt. (remanufactured). Wonder if I run cleaner through tank if that would help. I like techron but I see that other use seafoam. Also heard about drying additive to remove moisture. Any suggestions.I have long thought i have excess fuel prob.

Am I going to loose my drive shaft? Other than vibration and occasional 1st gear clunk, not hearing any red flags or urgent fix.

THANKS again Doug

Oh yea, I do have standard mechanical fuel pump.
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