87R problems

[jcas]

Here's the problem. I recently installed a keihin 38mm airstryker carb with cr reed cage on my R. The first time I took it out, the piston seized. I rebuilt it, and replaced the flywheel side crank seal to be safe. I jetted up to 185 main and 50 pilot. Took it out during break in and it froze again! The piston looks like it leaned out, like it was taking in air from somewhere. Also, both times I took it out, there was an extreme studder in 2nd-4th gears if I didn't have the throttle pegged. Kind of like it was bogging, like way too much fuel. If I didn't have the revs way up, the bike would even slow down and I had to downshift. Is there something I'm missing about these carbs? Any suggestions? HELP!!

[methyman]

First off how did the piston look? Heres a chart Eric Gorr Piston Chart (http://www.eric-gorr.com/techarticles/pistondiaguide_ta.html) . What did you plug look like? Was it a Wiseco Piston or Pro-X? WHat was the piston to cylinder clearance? Did you do a leak down test on the motor? It could be any one of these little things or a combination of a couple.

Later

Matthew

[jcas]

The piston had scratch marks on the right side exhaust side, looked like heat transfer. The piston is pro-x. ESR did the bore work, I'm not sure about the clearances. I did not do a leak down test, but I'm going to try that baby powder around the suspect areas trick and see what happens. But why would the motor bog and want to shut off if not pegged? First and second are ok, but after that if it's not reved way up the motor loses power and wants to shut off. My jetting is not soo rich that I would expect that, but even as I jetted down on the main it didn't make a difference. The only things I changed when I put on the new carb was from the reed valve back, so I'm suspecting the problem is there somewhere. HELP!!

[methyman]

CHeck the gasket and make sure fuel is mixed 32-1 with good oil. It does sound like the jetting is way too rich.

[beerock]

the studder is from the motor being WAY to lean Holding the throttle WOT to get past it is exactly why you seized it again. what needle is in this carb ???



you could be leaking from a couple areas, carb boot, intake gasket, your crank seal on the right side(if it was this side the plug would be black and burn tranny oil), base gasket or possibly from the center cases.

you have to do a leak down test on the motor and pin point the problem.

when you have a airleak you can put a 200 main and it will be lean.

[jcas]

I put the needle at the 5th position and changed the main to 195 and the stutter was gone. It ran smooth from 1st thru 4th at mid throttle. I'm not going to push it until I have it checked for leaks. Should I change the needle or is it ok? The pilot is a 50, should I go up? I'm going to try a 195 and see how it runs. Thanks for the help.

[jcas]

The needle is a DGH and the plug was tan in color. It pulled even from start to 3/4 throttle. Thanks for any suggestions.

[beerock]

what size is the cylinder? is it a stocker or big bore?

even if its a big bore a 195 is pretty big unless you have a 350 even then its big.
when you put it in the 5th position do you mean you leaned out the needle(dropped the needle) or richened it (raised the needle)

[JTRtrx250r]

Originally posted by beerock
the studder is from the motor being WAY to lean Holding the throttle WOT to get past it is exactly why you seized it again. my 1st thought also, What was the compression and premix/octane?

[methyman]

If the cylinder is a stock cylinder just bored with that big of a main jet, you have to have a air leak somewhere. What size main jet was you using before you switched over to the cr intake and bigger carb?

[beerock]

if anything his main would be smaller using a larger carb

[jcas]

It's an ESR 310 on it's second bore. I was using a 175 main with a 60 pilot on the stock carb. I'm using 32-1 with 91 octane and 927 oil and a pump gas dome. I put the needle at the bottom (rich) position.

[pismoracer]

Leakdown test it!

[JTRtrx250r]

Originally posted by jcas
It's an ESR 310 on it's second bore. I was using a 175 main with a 60 pilot on the stock carb. I'm using 32-1 with 91 octane and 927 oil and a pump gas dome. I put the needle at the bottom (rich) position. It dont say your location, but this is winter...winter and 927 DONT MIX, it says right on the bottle it seperates in cold weather, we've all had bad luck w/ winter flattrack and 927 around here ...not saying thats the prob...but it sure wouldnt help

do you know what the compression is? if its too much for pump gas...Im starting to see the possible probs

you definitly need to take a compression test, and a leakdown test..,

[wilkin250r]

Originally posted by beerock
if anything his main would be smaller using a larger carb

How is this possible? His main jet should be larger for a larger carb.

Carburetors work on the venturi effect. Air passing over a hole will produce a vacuum up through the hole into the airstream. The amount of vacuum (which would directly correlate to the amount of fuel) is dependent on the speed of airflow.

If you're trying to pull a large amount of air through a small carb, the air must travel very fast. If you get a larger carb with a larger air passage, the airspeed is slower. (Imagine if you had a 300mm carb, 12 inches. How fast would the air be going through with a stock 250 motor?) Slower airspeed means less venturi effect, less vacuum. If you have less vacuum, you need a LARGER jet to get the proper amount of fuel.

[jcas]

It ran fine for 4 months with 91 octane. The problems began when I got this new carb(15 minutes after!). Could it be the ignition system? I'll check the compression and the crank seal. Then I'll get a leak down test. People are telling me I need a new bike, but I'll never give up on her!!

[JTRtrx250r]

it could be your electrical system, but it sounds lean like an airleak, did you check the intake manifold around the rubber/metal for cracks? if its been since you swapped the carb...Im wondering if the floats are set way low or something, there are many variables..but take things 1 at a time

and yeah...dont give up on her!!

;)

wish ya luck!!

[beerock]

Originally posted by wilkin250r
How is this possible? His main jet should be larger for a larger carb.

Carburetors work on the venturi effect. Air passing over a hole will produce a vacuum up through the hole into the airstream. The amount of vacuum (which would directly correlate to the amount of fuel) is dependent on the speed of airflow.

If you're trying to pull a large amount of air through a small carb, the air must travel very fast. If you get a larger carb with a larger air passage, the airspeed is slower. (Imagine if you had a 300mm carb, 12 inches. How fast would the air be going through with a stock 250 motor?) Slower airspeed means less venturi effect, less vacuum. If you have less vacuum, you need a LARGER jet to get the proper amount of fuel.

right:scary:

I was thinking about my badly engineered edelbrock 750cfm

[jcas]

Checked the crank seal and it looks fine, I didn't see any gas/oil around the seal or in the case. The manifold is brand new but I'll pull it off and check for tears. I put in a 195 main and I'm going to try it out tommorow. How do I check the carb floats? Is it at all possible that it was just the jetting? Is 2 stroke jetting that crucial? Thanks again for all the help.

[JTRtrx250r]

No worrys on the help...thats what this is all about and all we can do is try and help troubleshoot probs, but its only easy w/ the obvious haha

You wont really be able to tell if the motors sealed just by looking at it, a leakdown test pumps about 6lbs of pressure into the motor...,if and ONLY if it holds that pressure for 6-8 mins is the motor sealed, if not it will lose psi fast ,or gradually..but it needs to hold and not leak real fast, it will let you know by the gauge dropping...then you need to find out if its an intake,case, seal etc leak. You can make your own leakdown tester (do a search) for about $15-$20

Whats it do w/ the carb that was on it b4 you swapped it?

And YES...lean jetting is VERY crutial!

[jcas]

O.k., there's got to be an airleak. After a proper warmup, I ran it with a 195 main all out for about 30 seconds and then killed the motor. I checked the plug and it was ashy white. If I stay below half throttle, the plug is a nice dark tan color. Can it be the ignition? I first sprayed wd-40 around every seal to try to bog the engine, then carb cleaner to try to get motor to react. No changes. It's going in the shop tommorow for a leakdown test. I'll let you guys know what's up when I get the bike back. (On a side note, that 38mm airstryker had the front end coming up thru 5th gear. Damn I want to ride!!!! AArrrggghhh!!!!!)

[beerock]

how is your ground?

[jcas]

Haven't checked it, but I will. Could that be causing the problem? What exactly should I look for?

[beerock]

Originally posted by jcas
Haven't checked it, but I will. Could that be causing the problem? What exactly should I look for?

make sure the ground is contacting a nice clean spot on the frame(metal to metal)

[jcas]

It's grounded good. Took it to the shop to have a leakdown test done. If no leaks, then it looks like the cdi box. If that's the case, what's the best cdi? Oem or aftermarket? Any certain brands? Thanks.

[jcas]

No word from the shop yet. If it is the ignition, do I need to change the cdi or just the coil? Do I have to change the stator? As far as the cdi goes, I heard the 89 cdi is better. Can I just slap it on? What about the cr cdi? Thanks again guys.