wow.... lots of views but no comments....

so the bike starts and will idle, sounds normal i guess...... but even after i have let it warm it still wont rev, i can open the throttle but only a very small amount and the bike will increase in revs but if i continue to open the throttle it will start to die.... starts to rev slower and if i keep opening the throttle it will stop. both cylinders are firing.... fuel is dripping in as i can see it through the fuel filter i have put on.... i did not put the fuel pump back on so it is only gravity fed but the pet tape is well above the carb.

i did however expect to see the filter completely full of fuel but that is not the case, but there is definetly a constant amount of fuel in the filter, surely enough to feed the carb.

why wont it rev....? what have i done wrong...? what could cause this as i dont have any idea....?

the only other thing that i think might be wrong....? but not really sure.... is the vacuum level, doesnt seem to be much of a vacuum at idle when it should be at its highest... right
i checked for leaks and all looks good, the two nmanifolds are almost new and look it to. as i said i checked for leaks but only by looking at ever thing and they look like they are seated well and shouldnt have any leaks..... how else can you check for a vacuum leak....?

what could cause a weak vacuum level if there are no leaks....?

You mentioned that the rear exhaust pipe was cold. Pull both plugs and clean or replace both of them. Fuel is getting to the front enuf to get it hot so let's get the rear jug firing first.

Doc

DocShadow wrote:
You mentioned that the rear exhaust pipe was cold. Pull both plugs and clean or replace both of them. Fuel is getting to the front enuf to get it hot so let's get the rear jug firing first.

Doc

hey Doc.... i did say that and i did find out why it wasnt.... the slide in the carb was stuck.... soaked it and pulled the slide and membrain out, cleaned them both and now both cylinders are firing but still wont rev much.... wouldnt even be a 1/4 of a turn....?

so it starts, both cylinders.... will idle nice, sounds good.... then i can increase the revs a little but before i get any where near a 1/4 throttle it starts to die....

I know you said the slide was stuck and you fixed that issue, but is the slide moving with Vacuum? You may have a bad diaphragm that is not allowing the slide to raise with vacuum when throttling up. Try reaching into the carb throat with a long screwdriver lifting the slide a bit while throttling up. If the helps replace the diaphragm. If it don't help you may have to disassemble the carb and do a good cleaning. After all if it was bad enough for the slide to be stuck, the insides are likely to be all gummed up also.

ok.... i know i should have been thorough when i pulled every thing off to get to the carb...... spending a little more time cleaning and then checking it was working in opperation.... huh

i did seem like an obvious fix and the cleaning i did made a huge difference, the carb looked clean as could be and it all seemed to move and work.... but i did not check it when i popped it back on the bike, i just put every thing back on expecting it to work.

it is 11.30 pm so hopefully tomorrow i will do it all again and see if the throttle moves it.

thanks Davej and Doc for your reps

hermit, have you considered your exhaust back pressure - either too much or too little? very little back pressure could scavange your intake charge some. kinda doubt backpressure would be the entire issue but it's worth considering along with everything else you're looking at.

Lrdstar wrote:
hermit, have you considered your exhaust back pressure - either too much or too little? very little back pressure could scavange your intake charge some. kinda doubt backpressure would be the entire issue but it's worth considering along with everything else you're looking at.

hey Lrdstar.... thanks for your thoughts
i have thought about my exhaust pipe design..... i dont want it to be the cause..... but i know there can be issues if the reversion wave is not timed properly, i did spend a lot of time reseaching exhaust systems but with out some high tech equipement i could only make a good guess and then will see what happens.... fixing issues as they pop up.

i tried to stay fairly close to stock spec's with a small increase in dia. as i have more air and fuel..... i also tried to have the best of both worlds by incorporating the vacuum activated valve which opens the flow as the engine revs., but yes it was only my best guess..... i really hope i find gummy jets or some thing, i dont want my pipes to be at fault.

but dont get confused.... we dont want back pressure.... a well tuned system with free flow pipes is what we want.

here is just one article, i read many and once you start it becomes addictive.

http://650ccnd.com/exhaust.htm

masterhermit, The vac opp valve you have in the exhaust, any way to verify that it is opening as your rpms try to climb. Maybe causing a restriction and messing with the vac signal for your slide in the carb. Ride on, Mike

Really amazing work.