Carb causing engine compartment heat.

[iceman]

I have a 750 double pumper that causes the exhast to get so hot it causes vapor lock. Changing carbs gets rid of the problem - so I know it's the carb. But I can't figure out what could make a carb do that. They are both jetted the same and I've sprayed starting fluid around the base looking for vacuum leaks and didn't find anything. Anybody got any ideas as to what it coild be. Thanks.

[Fox_hunter42]

spray around all seams on carb. sound like a vacuum leak. Accelarator pump or power valve?

[twisterf5]

it may be jetted the same but one is lean. a engine that lean does not have enough fuel to make a big bang that blows out the flame instead it stays in the pipe causing your problem. if that make sense to you. had the same problem jetted up and it fixed it.

[iceman]

I've sprayed starting fluid around all the seams - no change in RPM. I went up three sizes in jets - no change.

[dirtracerl77]

I had one that did this. It ended up being a restriction in one of the air bleed passages. I could put the biggest jet I had in it, it would still lean out under wot.

[DaveBauerSS6]

Float level too low.
Main bleed dirty/ restricted.
Power valve stuck closed.
Incorrect metering block gasket.

[let-r-eat]

Dave is giving you good advice.Does this carb idle fine on the engine? Are the transfer slots under the butterflies square when you remove the carb after you set this intended idle?

[iceman]

I've gone through it, made sure passageways were clear, gaskets were right, adjustments were right, and no leaks. The headers get to over 700 degrees (max of my thermometer) in less than a minute at idle, faster than that if you rev on it. Put my other carb on there and after 2 to 3 minutes headers are less than 600 degrees. I've talked to the manufacturer and we've decided that I should send it back to them and let them figure out what the problem is. Hopefully, they will let me know what they find and send me the offending part so I can use it for target practice (after all the headaches it's caused me, I think it deserves capital punishment). Thanks for all the help, I'll let you know what I hear.

[diggindirt]

Check to see if the metering block is the same as the other. I had this issue and bent three valves due to high EGT's. One carb would do it the other ran fine. took the metering blocks off and made sure all the orfices were the same size (they weren't), made them match the other good carb and the it performed like a champ. Found all of this on the dyno while playing with fuel curves.