GM Top Engine Cleaner

[Timothy B.]

Anyone ever used the GM top engine cleaner on a small block to remove carbon deposits around intake valves, combustion chamber, etc.

How does it work and what's the correct procedure using this product so no engine damage gets done. From my research it seems this product has evolved over the years is that true.

I have also read about a product called seafoam that is supposed to do the same thing.

The reason I asked is because I have tuned my 67 300hp engine to perfection and it runs great but the idle seeks at 650RPM until the plenum gets good and hot. I am convinced there are carbon deposits restricting idle flow at this low RPM causing uneven fuel distribution. The problem is easily masked by increasing the throttle but that's not good enough for me. :-) I have never had the heads off but the intake has been off by me and is very clean throughout.

All thoughts are appreciated.

[Joe R.]

Re: GM Top Engine Cleaner

Timothy,

Using these products won't harm your engine so try the Seafoam or the GM cleaner and see if it does any good.
After that fails concentrate on your carb as the idle is effected more as the throttle plate pivot shafts wear in the aluminum based material and cause most idle problems. The carb can be fixed by a machinist or someone in the carb business. All this is assuming the carb has been installed correctly and all idle air circuits are clean and free flowing.

JR

[Edward J.]

Re: GM Top Engine Cleaner

Tim, years ago when I worked as a GM tech, we routinely used Top Engine cleaner for carbon clean-up, the best way to approach this is, start the engine and warm up to normal operating temp and raise engine speed to 2000/2500 and pour some into the top of engine and let it stall out engine and let sit over night, then come out in the morning open the choke wide open (hold open with screwdriver) and start engine and warm engine then hold throttle open to about 1500/2000 and start pouring the rest of can into engine slowly till empty. This the correct way to carbon clean the engine. then when finished you take a second can and pour into fuel tank and fill=up and drive this can through the engine. MAKE SURE YYOUR DOING THIS OUTSIDE.

[Mark E.]

Re: GM Top Engine Cleaner

What do you mean "the idle seeks at 650RPM"?

Unsteady idle speed?

[Joe L.]

Re: GM Top Engine Cleaner

Anyone ever used the GM top engine cleaner on a small block to remove carbon deposits around intake valves, combustion chamber, etc.

How does it work and what's the correct procedure using this product so no engine damage gets done. From my research it seems this product has evolved over the years is that true.

I have also read about a product called seafoam that is supposed to do the same thing.

The reason I asked is because I have tuned my 67 300hp engine to perfection and it runs great but the idle seeks at 650RPM until the plenum gets good and hot. I am convinced there are carbon deposits restricting idle flow at this low RPM causing uneven fuel distribution. The problem is easily masked by increasing the throttle but that's not good enough for me. :-) I have never had the heads off but the intake has been off by me and is very clean throughout.

All thoughts are appreciated.

Timothy------


I used to use the GM Top Engine Cleaner a lot. There used to be two types. One was a "pour in" type. The other was in a spray can and you sprayed it in while the engine was kept running, using the entire can. I preferred the spray can type. However, I don't know if it's available anymore. The last part number I can find for the aerosol is GM #12345089 but it's discontinued. The pour-in type is GM #1052626.

[Edward J.]

Re: GM Top Engine Cleaner

Joe, I don't believe the spray is still available. I like both, but the pour in method is what GM recommends. for the first use, by pouring through the Carburetor till it stalls this will soak the valves and pistons and then let sit, the longer the better, and then slowing pouring the rest of the can while running will help clean up carbon.

[Paul D.]

Re: GM Top Engine Cleaner

Edward is dead on as to how it was used in dealerships "back in the day" . We used it to repair what we called "chronic spark knock" and it usually did the trick. Also, do not take lightly the warning about using OUTSIDE! You are going to produce a lot of smoke. We used to head for a rural area upon start up to blow it out good. In today's close neighborhoods, you will not be well liked after this procedure.

[Timothy B.]

Re: GM Top Engine Cleaner

What do you mean "the idle seeks at 650RPM"?

Unsteady idle speed?

Mark,

It's a lean surge up and down, after a drive when the plenum is good and hot the idle is steady, I believe this is because the hot plenum vaporizes the fuel load causing the distribution to be better. The carburetor is in top condition with a new primary throttle shaft and bushed throttle body, also has new secondary teflon bushings in that shaft. It's a sweet 3810, did I mention the IFR's and IAB's have been modified for 6-32 and 8-32 brass set screws. These carbs are rich and with a little attentiveness to the idle circuit the engine runs much better. This condition I am talking about exists with the factory size air bleed and idle feed holes so that's not the issue.

I am fairly convinced it's just carbon in the back of the intake valves causing this fuel distribution issue at this slow idle. If you do some reading on the internet there are quite a few issues associated with the build up of carbon even on new cars. I can't recall ever discussing this on the forum but with these old cars it's probably a topic that some may benefit from.

[Brian M.]

Re: GM Top Engine Cleaner

My 67 327/300 4 spd is happiest at 750 RPM.

[Timothy B.]

Re: GM Top Engine Cleaner

My 67 327/300 4 spd is happiest at 750 RPM.

Brian,

I can idle my brothers L-79 at 750 RPM no problems, completely different camshaft and valve timing. If you open the throttle blades and send more air through the carburetor the 300hp engine does not hunt/seek.

[Peter M.]

Re: GM Top Engine Cleaner

Hi Joe,
I thought the 1052626 was the spray in.
Kind Regards

[Leif A.]

Re: GM Top Engine Cleaner

Anyone remember "steam cleaning" your combustion chambers. We used to warm up the engine, remove the air cleaner, hold idle at around 2000 RPM and slowing pour water down the carburetor (revving the engine as necessary to keep running). Seemed to work just fine.

[Paul D.]

Re: GM Top Engine Cleaner

Transmission fluid also works well.

[Joe L.]

Re: GM Top Engine Cleaner

Hi Joe,
I thought the 1052626 was the spray in.
Kind Regards

Peter-------


Yup, you're correct. I was incorrect. The GM information I was referring to was "sketchy" as to the type and I interpreted it as being a pour-in. It's an 18 oz aerosol.

That being the case, I don't know what the current part number is for the pour-in type. The original part number was 1050002 which was superseded by 12345088. Both are discontinued. There may be a new number but I don't have it.