What's new
CK5
Register an account today to become a member! Once signed in, you'll be able to participate on this site by adding your own topics and posts, as well as connect with other members.

350 won't idle after vortec head swap

F

fatcat92

Registered Member
Joined
Apr 10, 2015
Posts
20
Reaction score
0
Location
Canada
Hi,
I have a 79 k5 with a 350 and have just put in new GM 060 vortec heads with a new edelbrock performer RPM and used my old Holley 650 carb, and old HEI distributer.

I used the 501SD head gaskets and the manifold gaskets from the MS9800T2 kit. After cleaning them I used my old pushrods and old self-aligning rocker arms, and I already had center bolt valve covers so I used those aswell.

Now my first problem was I couldn't get the thing to fire properly and I tried swapping caps and the chip but I found out I needed 0.708" reach on the spark plugs and I was going by the normal 0.4" or so of the original, so I ended up going with the TR5's from NGK, I thought this would solve all my problems.

Now it runs fine and doesn't misfire at all, but I can't get the damn thing to idle! It will start great and if I rev it out it will keep running, but pretty well as soon as I let off it will die. I had someone in the engine bay hold the choke and we had it idling at around 3000RPM! What could be the problem?
Vacuum leak? Fuel issues? It sounds like it runs super lean. Could my carb be giving it the problems? It worked good before.

I tried premium in it today by putting it directly in the carb after draining the regular 87 stuff out of it and plugging off the hose to the fuel tank, but no go, it seems to run better but still can't get it to idle.

Has anyone else done this swap and had to change anything related to the carb? Bigger jets maybe?

EDIT: Topic title got submitted before I was done typing... supposed to be "350 won't idle after vortec head swap"
 
Vacuum leak.

Make sure valves are adjusted correctly.

Then go around with some carb cleaner and that little bastage straw sprayer. Light spritz around every thing you just changed, a little at a time. The rpm will change when you're close to the leak
 
I can't get it to idle at all though, would my best bet be to just tear it all down again? I did use the intake gaskets twice and used RTV the first time on the end seals and water jackets, but I had the wrong bolts so I never bolted it on and had to clean all the rtv off.. and heard putting the rtv just on the end seals would be better. The reason I changed these heads was because of an overheat and and small crack in the heads and blown head gaskets the engine side was flat, and everything elsed seemed ok, so I didn't take the block in. Could the heat have damaged the carb at all to cause this?
 
What rpm intake do you have. Be sure it is for the Vortec heads.
 
I'm curious if reusing the gaskets caused issues
 
I put them on dry aswell, should I have used a thin bead of RTV around the intake and water ports?
 
I'd do the carb cleaner trick first. If you don't find it upstairs I'd be inclined to pull the intake and see how it sealed and if the intake surface of the heads are flat.
Had this exact issue once and was not sealing between the intake ports
 
I am wondering if it is an issue with me using them twice and the fact they are out of this kit that I was told was good MS98000T

I am thinking of getting the regular MS98000 gaskets after pulling it, I don't think it is anywhere above the intake and as far as testing it I have no clue Id have to rev the shit out of it to keep it running. I almost have a feeling it has to do with reusing those gaskets
 
I didn't have any issues after a vortec head swap on my 74

I used the rubber oring style intake gaskets when I did my swap. IIRC they fit on the heads a certain way. They were also put on dry for the exception of the ends which are RTV only.

Sure sounds like intake leak, for that amount of work I wouldn't reuse the gaskets.
 
I just went ahead and pulled the intake off and cleaned it up for the most part and will be going in the morning to get MS98000T again and I'll try from there
 
Im no engine internal genius but if it were me Id look at gaskets for a vacuum leak and check pushrod length to make sure you dont have valves hanging open.
 
I agree that it definitely sounds like a massive vacuum leak.
 
If the Edelbrock has a spread bore carb base and your putting a Holley carb on it that has a square bore base,it'll probably bolt up OK,but will have massive vacuum leakage..you need a plate like this to mate the two..

carb adapter plate.jpg
 
Alright, I have it all back together I am just waiting for the RTV to dry on the end seals. When I was torquing the bolts to 11ft-pounds on the intake I clearly remember torquing these to 25-30 before... I think that must have been my main problem. If I overtorqued them wouldn;t the gasket not seal properly?
 
I feel it would not. Look at the distance between the 2 closest intake mounting bolts. I can see it (the intake mounting flange) flexing in the middle with that much over torque. Not enough to see visually, but certainly enough to cause a vacuum leak.

Fwiw, the only gasket I ever reused was a HD primary case gasket made to be reused.
 
FWIW, I'm not sure any of the intake gaskets for Vortecs are very good, at least the ones that require minimal torque.

Totally agree with Big Ray about distance between the bolts being a potential issue, but when trying to find the "newest" version of the Vortec intake gaskets (they are on the 3rd design, think they knew there was a problem?) I found that FelPro 1255 is available and designed for the Vortecs, but it's a more "standard" design. Just flat gasket material. .12" thick comes to mind for some reason, I'll compare thickness with the gaskets on the motor now.

I'm going to try those this time. When I take my intake off the present motor, I'll know what shape the intake manifold gaskets are in, which are one of the older variants, I believe with the blue silicone sealing portions.

13ft lbs is too little for most ft lb torque wrenches to accurately measure, you really need an in lb wrench and convert that measurement to ft lbs.
 
You must log in or register to reply here.

Latest Posts

Top Bottom