Flathead cutting out

So I have a Dover flatty that ran great for 3 races.. now it's cutting out in the mid Rpm range both loaded and unloaded.. Ideas? Help,


Dawg 89
Its will act funny unloaded . what have you checked or changed ?
They also are not tuned too run at mid throttle .
Changed jet from 56 to a 60.. going to try a new diaphragm tonight I really think it's fuel related as it will rack to about 4k then cut then rev again higher but ran a lap down the street and it seamed intermittent through the pull.. I lost the header last race and it was very Poppy and choppy while it was loose. Thought this was only problem but replaced it and now am fighting this cutting out..


Dawg 89
60 is pretty big . Over rich will cause that .
A plate engine or unrestricted?
Is the plug indexed properly?
As when the valve hits it , it closes the gap , same result .
Which plug ?
Ngk plug. It had about .030 gap changed plug and diaphragm and seems ok now.. it's an adult engine. Was at one point gold plate engine but I've always been told a gold plate engine is built like an adult and they stick the plate in. Dover carb and engine..triple a card not marked with an r for restrictor carb

alvin l nunley

Site Supporter
.056" – .060" is a 14.78% increase in hole size (flow)! That's huge! It'll be interesting to hear if that cures your problem.


Dawg 89
Honestly , think you need to lean it back out . Simple fix if what you have done ends up not curing the problem .
The surface gap plugs are ok , i had issues though . fine in my 140 johnson .


Definitely agree with Triton03 put a 49 jet in it. Back when we ran gold plate we used a 52, blue plate a 56 and purple a 62.


Site Supporter
Agreed with above. Put a 49 or 50 jet in it and run your screw 1 1/2 turns off the seat as a starting point. I never cared for the surface gap plug as they were a bugger to start without a buzz box. Make sure you have no exhaust or intake leaks as well. Carb and tank gaskets both. If that was a true gold plate at one time that should be more than enough jet to run it properly. It usually ends up being a diaphragm or dirty alky. Check your coil air gap as well make sure it’s not out of sorts.

alvin l nunley

Site Supporter
Here's something far out; my friends 130, 2 cycle, as he approached the end of the straightaway, would start missing, cutting out. In the pits, they started the engine, attempting to diagnose the problem, and I noticed the the boot on the spark plug wire was kind of dancing around. My theory, just a loose connection to the plug. Far out I know, but it happened.


Site Supporter
It sure sounds like the pick-up tube, or metering holes are partially plugged if you are running that large of a jet in an unrestricted engine.
.048" with a loop pipe and .050" with a straight (muffled) pipe should get you close.
Pull the tank and carb apart and clean it thoroughly.

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