fuel starvation

[gwcrim]

So Mardy, the RD with Spec II porting and pipes and stock carbs isn't running 100%.  Ignition is points with coils from Spec II also.  I spent lots of time doing my best to set the points up correctly.  Seems to run well most of the time, far better than it had been while I dealt with jetting.  But when I'm twisting the throttle, I have some issues.  I live in the Ohio River Valley and ride up and down some pretty steep hills.  The petcock is stock also. 

Could I be experiencing fuel starvation?

If so, is there a way to mod the petcock to flow a bit more?

[Jspooner]

What are the issues?

[m in sc]

does it sputter or?

[SUPERTUNE]

I sell a petcock conversion from a Raptor 660 for the 400's that will cure any fuel petcock issues.
Did you use oem points or aftermarket crap? If a RD350, I mod the backing plate to use the 400 points.
Do a coil relay mod and make sure charging system and battery is strong if staying with points.
Much better to convert to cdi in the long run.
Chuck

[gwcrim]

The issues are sputtering and pinging.  Not necessarily at the same time.  I've tried a larger main jet and that didn't work.  I haven't spent much time riding it to really get a good feel.  I need to do that but the weather and life just don't seem to cooperate.

Knowing me, I probably put the cheapest Ebay points on it.  I know that I ought to do a CDI but that's not in the cards at the moment.

The battery is an alarm battery.  No idea about it's condition except that the bike does start and run.

What's a coil relay mod?

[m in sc]

check the fuel tank cap vent, make sure its breathing. have you lined the tank or swapped the cap?

to verify, take a line off the petcock, set up to flow into a can. clamp off other line to carb (or will suck air and mess up the test). leave fuel cap closed.

turn petock on, check for flow over 2 minutes. measure amount of fuel.

then, pour that back in tank.

leave fuel cap open. test again. 

if it flows more second time, check cap vent. if it kinda sucks both times, check petcock.

remember, the needle seat on these carbs is about  a 2.0mm orifice wide open, that's usually the biggest restriction.

IF the main jet is larger than the needle seat, you need to up the seat size. however, that's only usually noticeable at wot for a sustained run.

[gwcrim]

Fuel flow seems good.  I think I'll try a bigger main, but I'm already at 290.

I rode it a bit yesterday.  It starts right up and runs along fine in midrange.  Crack the throttle and it goes flat or maybe just running on one.  If I ease into the throttle it will take it.  Winds out until about 8500 then pinging starts on the left side.  It just doesn't seem consistent.  Except the pinging.  Get the revs up there and it always pings but just on the left.

[Jspooner]

Double check your timing before making more jetting changes.

[m in sc]

raise the needle a clip. see if it gets better. thats my guess.

[gwcrim]

Both good ideas.  I really hate messing with the points so I imagine that's where the trouble is.  Murphy's Law and all.

[SUPERTUNE]

You never did say what model you have...
Chuck

[gwcrim]

It's a '75 RD350, Chuck.

[SUPERTUNE]

Fuel flow seems good.  I think I'll try a bigger main, but I'm already at 290.

I rode it a bit yesterday.  It starts right up and runs along fine in midrange.  Crack the throttle and it goes flat or maybe just running on one.  If I ease into the throttle it will take it.  Winds out until about 8500 then pinging starts on the left side.  It just doesn't seem consistent.  Except the pinging.  Get the revs up there and it always pings but just on the left.

290 main jets means your still on stock bleed needle jets?
You should go to the primary needle jet conversion (dave f mod)
I would be using RZ manifolds and crossover tube (or my TSR/Barlow boost bottle) (no way are you using stock airbox with that big of jets)
Then you would be in the 200 main jet range.

Ignition/charging system has to be right first.
Chuck

[m in sc]

true.

Ive said it many times:.. most jetting problems are electrical. lol.

[economan]

true.

Ive said it many times:.. most jetting problems are electrical. lol.

Classic !!