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the new m37 i got runs and starts perfect at 25/30 mph any higher 35/45 it starts to sputter and kick a little. does not pop .. changed fuel filter but didn't seem to help.. starts right up and idles great.. has original system. nothing seams to be modified.any help would be great.

Is this only under load? Hot or cold?

Where is the filter located that was changed, In line or in the fuel tank?

kind of under a load...it has a inline 5/16 filter i changed that.

"Kind of under load.." So if you rev the engine to top end speed in neutral it does not sputter or sputters less?
It sounds as if you have a fuel or ignition problem. Is the spark good on all 6? Timing ect..? My guess is your sputter is either caused by poor fuel delivery or ignition break up at the higher speed. I am leaning towards a fuel/carb issue sine you said it is more of a "Kick". Was there much crud in the old filter?

i can sit in neutral and rev it up and its seems ok. soon as your driving its when it starts to buck when u are past 30/35/ maybe it does at this speeds but it is not as noticable, probley should drain the tank

clean your points and distributor cap, weak spark can cause it to run like you're describing. also make sure the distributor mechanical advance is working, the rotor should rotate smoothly something like 20-30 degrees, with spring tension pulling it back. if it binds up or won't smoothly rotate you'll have to pull it and clean it. i did this to mine, and it made a whole world of difference

thank you i will try that

10-4. Check that ignition out like Isaac said and make sure the fuel system is clean. Has to be one of the two if all else is in order. Keep us posted. good luck.

I just got my m37 project plated so I could drive it on the road. Idles great, runs as smooth as silk, then dies at 30 mph. Took the carb apart(it had sat for over a decade).It was full of crud. The pump plunger is seized, the plunger leather is dried right out, the pump intake ball was stuck in the seat and the channel is plugged and I can't get it clean And to top it all off, the pump check spring is broken.
Hope yours is more simple to fix but that's what caused my problems.
Anybody got a spare carb?

sorry to hear the carb was so ruff point. I have some bits.

dont forget our carbs are different from the 230

Hi Robyn. I'll call you Monday

the spurting is there sitting there with the throttle to the floor. i don't hold it there i don't want to blow it up...

junkyardog wrote:i can sit in neutral and rev it up and its seems ok

junkyardog wrote:the spurting is there sitting there with the throttle to the floor.

all I can see is that poor 100lb big stroke crank supported by four little bearings, flailing around with 50lbs of flywheel and clutch hanging off one end as the operator revs it from 800 to governor and back

I never rev or race the throttle on my flatheads slow on slow off.
load it up and let it lug till it rattles

sounds like the high speed circuit is not working, the bearing could be a little jammy or the throttle pump is too tight in the bore making the vacuum signal too week to move the pump the required amount for the setup.

today's gas is only good for about three months

if its only a bit of crud you can try choking it out at a high rpm

i have one coming from vintage power wagons..by the time i take time off from work to bring it to the rebuild shop and then pay for it to be done it was about the same money to buy one from them..