79 Spitfire rev problem

JDXsand00s · Post by **JDXsand00s** » Sun Oct 23, 2005 8:28 am

These rev problems are getting redundant but nothing tells me what is wrong with me sled. I just rebuilt the 340 free air in my Spitfire and it will only idle. It has brand new pistons, gaskets, and seals from DK. It also has spark. Hypothetically, if an engine has compression and spark it should run with gas, right? When I take a squirt bottle directly into the intake and shoot gas in, my engine should rev over 3 or 4000 rpm, but it doesn't. It will idle for any amount of gas and also when the carb is on. The carb is completely redone as well. The snow is about to fly so any help in getting my sled to move would be greatly appreciated. Thanks.

harleysportster · Post by **harleysportster** » Sun Oct 23, 2005 9:28 am

The carb is completely redone as well.
What did you do exactly to the carb? Is the carb a mikuni slide, if so:
Fuel during idle is supplied by the pilot jet . As the throttle valve is opened wider for low speed, the fuel then enters the carb bore through bypass as well as t he pilot jet.
The main metering system starts to function when the throttle is opened about 1/4 of the way. From 1/4 to 3/4 open throttle, the fuel passes through the main jet and is metered in the clearance between the needle jet. Full throttle the fuel is metered entirely through the main jet.
It sounds like the carb has blocked passages.

JDXsand00s · Post by **JDXsand00s** » Sun Oct 23, 2005 12:48 pm

Every jet in the carb seemed to be open and fully operational. The jets were taken out and were obstruction free. Everything was flushed with carb clean as well.
Should the engine be able to rev up without a carb by just shooting gas straight into the intake?

harleysportster · Post by **harleysportster** » Sun Oct 23, 2005 7:12 pm

When you have it running and try to eccelarate, what happens. Does it stall, bog out and continue to run or run at idle speed with a wide open throttle. I don't know how the igniton advances on these engines, but if it is anything like the kioritz engines, they have a high speed circuit in the cdi and when they fail, it does the same as what you are experencing.
One other thing to check is the exhaust pipe for a blockage. Squirrells and rodents have been known to create nests in there

JDXsand00s · Post by **JDXsand00s** » Sun Oct 23, 2005 8:50 pm

I don't think that there is anything in the exhaust, but I can hold the throttle wide open and, as long as I supply it with gas, It will run at about 4000 rpm. I don't know much about cdi boxes so I don't know if it is bad, but I bet it easily could be. Would there be a way to check the high speed ircuit or is it just something that is assumed bad?

JDFanPa · Post by **JDFanPa** » Mon Oct 24, 2005 2:15 am

If you put crankseals in it and had the stator out it may be out of time if it was not reinstalled in the exact same spot. If the ignition timing is retarded to much it wont rev.

Another possibility but probably unlikely. I remember reading of a similar problem with a rebuilt motor and the pistons were in backwards.