340 CCW issues

[eppjd]

Both of my 74 400's started running like s*** this weekend, let me explain....

Rebilt walbro carbs for both of them before the season and they ran better than ever before (did have bendix carbs on). They start good and run fine until after the first 25 miles. One engine would lose power while holding it wide open (flat hard pack trail) and then it would regain power as if nothing had happened. After this weekend it happens more frequently and more later on into the ride, turn it off and restart it and it would be back to normal for a bit and then do the same thing. The other one started running like crap this weekend, starts fine all the time but the power drops for no reason on a good trail, then on the way back home I couldn't keep it running unless I fed it with the primer the whole way. Not a fun way to ride.

If anyone has experienced this before or has some tips and advice I would be more than happy to listen.

Thanks
Adam

[400brian]

Fuel filters and the screened pickup in the tank, Sounds like fuel delivery issues.

[eppjd]

I kinda thought so, however I put new filters on both this year (2 on the one with the steel tank). But the screen check valve could be plugged so I will try.

Still looking for other suggestions
Thanks!

[JD600]

Have you changed the crank seals? It could be that it is only pumping fuel intermittently. They are pretty cheap and not too hard to change.

DE

[eppjd]

Ok I will try spraying ether around the crank seal when it is running to see if it is not sealed.

Thank you keep em coming!

[JDFanPa]

Try pulling the fuel filter off when it craps out and blowing it and see if a bunch of brown crap. I have the same problem on my 74 x8 and after you blow through the filter it runs good for awhile its do to rust in the tank blocking the filter up even though the filter looks ok and the line is full it cant suck through it.

[DLDeere]

Warm weather? They get hot and get doggy.

Also, could be coils. A bad coil may run fine at first but then give a weaker spark after it gets warm. Cools off and then runs OK.

[JDFanPa]

I tell you my ideas on coils at this point in my life and ive been through workin on a sled for hrs to ride it 10 minutes til it dies for 25 of my 37 yrs on earth. Ive also worked on cars for 20 yrs now in new car dealerships. Its not often a coil fails usally when someone changes a coil they fix another problem and the coil is blamed.

[eppjd]

Follow up:

One had a dirty carb, runs good again.
The other sounds like seal(s)
(backfiring, dry plugs when it acts like its flooded)

My 75 800 still runs good so im happy with 2 out of 3 for this winter i guess