Thermoquad issue or MSD box?
 

I ran the Thermoquad last season and all was well until the engine lost a rod. I just got it running again this week and I'm having trouble, I'm not sure if it is the carb or ignition. The engine idles fine and run's around the pits like normal but under load it starts to break up really bad. The engine will RPM if you stay in it but it is not running right. If I run it about half throttle is seems good but once I really step into the throttle it sounds horrible. I took the carb apart several times and blew it out with carb cleaner, All the ports are free of obstructions. I really can't believe it is the carb. I also changed the MSD distributor to box harness, plugs and coil, No difference. I'm going to swap out the 6AL tomorrow. Is there something that could wrong with the Thermoquad from sitting for a few months?

Re: Thermoquad issue or MSD box?
 

Make sure you have enough fuel pressure.

Re: Thermoquad issue or MSD box?
 

Phillip: It takes very little to restrict a passage in a Thermoquad Carb (really all carbs are vulnerable by the Thermoquad is the worse in my opinion). I find some fine wire like armature wire and GENTLY work it thru all metering passage possible particularly the emulsion tubes in secondaries! Also check floats for height and see if they have absorbed any fuel.

I bring a half dozen extra race ready tested Thermoquad to the races in my trailer and ANYONE is welcome to borrow one to test for a pass ( No ... you can not take them with you home ).

Phillip: I will be up there for Nat's in July and can give you a hand and we can try a couple plus I have half the MSD truck for spares(Also recently tested) in my trailer!

GTX JOHN

Re: Thermoquad issue or MSD box?
 

What is the carb #? Sounds as if it is going very rich. Check and make sure the secondary jet O-ring gaskets are still there and in good shape. They can become brittle when they sit unused. Also make sure your needle & seat are working properly. Float drop should never be more than 1". Set the float height at 31/32". Jim

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Re: Thermoquad issue or MSD box?
 

Phil,
If it is a carb problem, it's most likely the secondary side. Check that the air valve is free and the stops set properly. Also look at the secondary vacuum pull off. Make sure the vacuum line is hooked to the proper port. There's two, make sure it's on the one furthest away from the pull off, it should have vacuum at idle. If this is switched the air valve will only open partially making the carb go rich like Jim said.
Good luck,
Let us know how you make out.

George

Re: Thermoquad issue or MSD box?
 

It was the carb, And does seem to be worse when I get it into the secondaries. The fun part was I put a 850 holley double pumper on to test, It was o.k with my 250 lb butt in the seat but Kelly had to put it into high gear to get the front end to come back down, Usually second gear will set it back down but this time it just went higher. The rear bumper is o.k but it was close,lol. Apparently the double pumper hits a little harder. I'll take a longer look at the carb this week. It was fine the last time the car ran late last year so it's a bummer that it had to act up this weekend.

Thanks for the ideas guy's.

Re: Thermoquad issue or MSD box?
 

Where's the pictures????

Re: Thermoquad issue or MSD box?
 

Just so long as it comes down before tripping the beams with your rear wheels! Jim

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Re: Thermoquad issue or MSD box?
 

George: Do you need the Vacuum Pull off............... I have run both ways and

it does not seem to make a Difference?

Re: Thermoquad issue or MSD box?
 

John,
I usually will get a stumble if it's disconnected or blown out. I guess if you have enough tension on the air vlalve spring you can run without it.
Must be that 100 + degree desert air you race in, here in the northeast it's usually cold and damp, and we all know how Plymouths run in the rain. LOL

It's great that your feeling better.
Take care of yourself,
George