ARRRRRRRRRRRRRRGH Engine cuts out!!!

This is driving me crazy!!!!!!!!!!!!!

As some of you know, I installed a 30mm Kehin PD Carb on my CRF230.

It has a 40 pilot, 1.75 turns out on the fuel screw, 37D slide, 85A needle, and a 158 main.

Engine has a 11:1 piston, BBR Cam, BBR Pipe and some mild head porting.

When running the bike at WOT, and then rolling off the throttle (not chopping the throttle) the engine momentarily cuts out, and then recovers. :D:naughty::naughty:

not a huge issue when in the dirt, but when mid corner racing SM, it could really ruin my day....can you say highside!!!!!!!!!!!!!!!!

Without hearing it, it's hard to say. But that's a BIG main.

:naughty: Hi what is the carb off ? is it a flat slide? are you shore it is a keihin? :naughty:

Cdaledh,

You have so many unique mods to your motor I seriously doubt anybody can snap to the correct answer for you. Let's just look at the symptom: "When running the bike at WOT, and then rolling off the throttle (not chopping the throttle) the engine momentarily cuts out, and then recovers." There's a lot we still don't know (symptom wise) but it sounds like it's possibly extra fat coming off the main jet & the end of the needle. If you have a needle with less taper on the last 1/4 of it you might want to give it a shot. A smaller MJ may be in order but hard to tell with a few words on a post.

To see if the MJ is fat try this: Get the bike nice & warm then go WOT & let off the throttle really quick. Does it give some small pops out the exhaust? If it does it for one second or less on decel your MJ is too fat. If it keeps sputtering then your slow jet circuit is too fat.

It could even be your MJ is fat & the needle is too lean at the end. Lean needle usually gives you snap the throttle bog though which I'm sure you wouldn't tolerate for long.

Larger carburators are hard to get the jetting right on & more sensitive to air density changes.

Are you also running a hot plug? A cooler plug is much better for reading than a hot one. A hot one can hide it being too fat.

Do you have access to an exhaust analyzer?

I know you know most of this stuff already but maybe something here will help. Hope you didn't get injured on the high side! :naughty:

:naughty:

I think it is the needle also. I think I will swap in the OEM 230 needle again and start tweaking. The needle in it now is the OEM XR250 needle...which has slightly more taper than the needle from the 26mm carb.

Throttle responce off the bottom is PERFECT, so I just need to play with the needles again.

I am running a colder plug too. DPR9EA9

Do you have the stock air boot? if no put it on and a135 main. :naughty:

I may have it!!

It feels like the engine actually runs out of fuel. I raised the float level a bit, and it does take longer for the "symptoms" to occur

I installed a fuel filter in the line. It is possible that the filter is not allowing enough fuel flow to keep the bowl full, causing the "hickup" when backing off the throttle from the pilot jet not being submerged in fuel.

ozditcher, please read the opening post in this thread. Not only is the air boot gone, but the top of the air box is cut away.

A 135 main is way too small!!!!!!!! I was running a 142 main in the stock carb with this engine.

Cdaledh,

Do you have access to an exhaust analyzer?

:naughty:

I wish I did!!!

There is a Dyno locally with one, but it is at a Harley Shop. While they will gladly take my money and run the bike on the dyno for me, they will not allow me to play with the jetting in their shop.

I may have it!!

ozditcher, please read the opening post in this thread. Not only is the air boot gone, but the top of the air box is cut away.

A 135 main is way too small!!!!!!!! I was running a 142 main in the stock carb with this engine.

You're not running an airboot?? Are you running a pod???

I think he was asking about the air box snorkle.

I am still running an airbox. The screen is gone, a UNI air filter is used (OE Replacememt) and I have cut out the top of the airbox.

I have the same carb and a 130 to a 135 main and my jetting is spot on. :naughty:

hmm me thinks it is ignition!!!!

got a Rev Box on order now!!!

Do the size of the holes in the emulsion tube affect anything?

I'm sure it would affect it somehow. The job of the emulsion tube is to mix air with the fuel making it frothy so it will atomize easier & stay in the tube better for quicker throttle response.

I think, guess, surmize & feel like bigger holes may make it ineffective as the air would just flow on thru & not mix with the fuel as well.

More holes of same size may make it more effective but again I'm just guessing. I think they'd (Keihin) have it optimized already. This would really be a trial & error thing.

You know you got me thinking about this now! I'll be back. :naughty:

Did you fix it yet? I run the same carb with a 130 to a135 main with race gas, what you need to do is run a plug test, go flatt out pull the clutch in and sutt the motor off. Pull the plug ,get a magnifying glass and look in the bottom of the plug not the top, check if it is black or tan black rich tan good. Let us know then step two, good luck :naughty:

done the plug check many times....still looks lean with the 158 and colder plug!!

This is why I am so puzzled!!

Air leak ,ignition timing,try stock carb,

ozditcher, I owe you a beer

It has a 40 pilot, 1.75 turns out on the fuel screw, 37D slide, 85A needle, and a 135 main now.

Holy smokes she rips. I went up to a 138 just for kicks, but the hickup started to rear it's ugly head....ever so slightly. She really pulls up top now. It's a good thing I ordered the rev box...I need it!!

What was screwing me up was the fact that with the OEM carb and the "power up needle" (C30f) you could run as fat of a main as you wanted....because the needle has almost no taper at the end. You really don't get anywhere near the main jet with it.

The 85A needle in the 30mm carb has a much more aggressive taper to it...so you actually get to use the main jet to it's full potontial.

Thanks for the assistance!!!

cdaledh,

Your jetting issue is what I had tried to explain in a number of posts. If you measure the last part of the "power-up" needle you will see that it is actually straight! Once you get over a certain size main jet( I crunched the numbers once but can't remember at the moment) it really will make no change because the needle diameter versus the nozzle I.D. becomes the restriction. It would probably run the same as before without a main jet!! On a stock 230, the main jet is metering the fuel at just after 1/2 throttle!! The restriction with the "snorkel" becomes the designed enrichener. Thats how they get away with a 102 main jet and still run fairly well.

Since you have a steep taper with the XR250 needle, You were more than likely just dumping too much fuel on deceleration as the main jet was just too big.

Certain carbs don't react like you would expect. I found that the Keihins on my old 250 R's were very similar in this same respect. I have been puzzled by this phenomenon for years. You could keep going up and up on the main jet, but the engine would never "four-stroke" like you would expect when in a way rich condition!! Just keep running clean! Very frustrating! Some carbs let you know right away after you have gone too big on the main. This is why I now depend on the A/F analyzer. Even with the 132 main in my stock 230 it seemed to be just about perfect. Hooked it up to the A/F and learned a thing or two again. 120 is all they need on the main(stock) Very odd, but sometimes difficult and frustrating to jet by seat of the pants like you have become used to sometimes.

I am happy that it is running more to your liking!

Mike

A large Fosters will do. Hope to see you at a supermoto race. :naughty:

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