Author Topic: Blubbery at 3/4- Full throttle (Read 7019 times)

pinned250r · « **on:** May 05, 2014, 02:25:50 PM »

In attempt to make this site busier in the "New Posts" section as well as just the general forum, im going to start putting ANY problem i have here, even if i know the solution(or think i do lol).

Finally got to take the R's out this weekend for a dune trip! My wifes that i built this winter ran amazing, i did a little tune work on it down the road, and said its good enough for now(slightly rich).

My R, that i didnt really touch this winter, other than cleaning up and adding some support to motor mounts, started acting funny. The last ride of the season last yr i finally got it dialed into a good rideable spot. This time, it started almost cutting out at about 3/4 throttle, until i cleaned out. At first i thought i was starving it for fuel, so i went up on the needle clip, that didnt do much for it at all. So then i went up on the main, and i definitely went the wrong way. Everyone else was ready to leave the dunes at that point, so i didnt get a chance to go back down on the main, but hoping it'll clear up.

Anyone have any expereince with this? It sounds like a non warmed up 2 stroke does if you get on it, start it, and take off.

PORTED R · « **Reply #1 on:** May 05, 2014, 02:33:48 PM »

Main jet controls 3/4 to wide open in the carb circuit
Drop the main one size at a time , in tell it clears
Also perform a plug chop at wide open ,to make sure your not to lean

pinned250r · « **Reply #2 on:** May 05, 2014, 02:40:13 PM »

Good deal man, thats my next step. Thank you!

Colin

C-Leigh Racing · « **Reply #3 on:** May 05, 2014, 02:43:01 PM »

What ignition system you using ?.
Check the silencer & make sure the core not broken loose, fell down & blocking the outlet.
Check those carb vent tubes,,,stopped up

.
Check float level.
Check compression.
Smell the exhaust smoke,,,

antifreeze smell ??.

If your running OEM ignition, my bets on that messing up at 3/4 throttle.
Neil

pinned250r · « **Reply #4 on:** May 05, 2014, 02:49:33 PM »

Dangit...Neil now you got me all worried. I do have OEM ignition, and its no big deal to change anything out as i have spares of everything.

Vent tubes are brand new, but i will check them.

Float level is right where it needs to be on 40.5 Keihin.

I will check the silencer, didnt even think of that....

Exhaust is solid as is compression.

I am going to play with the jetting a little before i go swapping ignition parts though. Because if it is ignition, its time to start saving for a CR

Rupp250 · « **Reply #5 on:** May 05, 2014, 03:47:42 PM »

Shake that flywheel like a salt shaker. Then drop it like its hot. HAha

Probably sounds like it has rocks in it................

But I would go down on the main first.

pinned250r · « **Reply #6 on:** May 05, 2014, 03:52:23 PM »

Haha i just installed that flywheel!

C-Leigh Racing · « **Reply #7 on:** May 05, 2014, 06:31:37 PM »

Well, I aint saying I know nothing, just what my hands have touched over the years on 250Rs.
Neil

pinned250r · « **Reply #8 on:** May 06, 2014, 05:04:28 PM »

Could the float be too high? As jb too much fuel in the bowl? Plug is showing lean.

pinned250r · « **Reply #9 on:** May 06, 2014, 06:16:19 PM »

Compression is only 150# should be about 200#, also I wasn't gaping plug correctly to builders spec. Thanks rob at RB Racing!

dirtyd · « **Reply #10 on:** May 07, 2014, 09:38:14 PM »

sounds like the same thing I did last year. When at WOT it would cut out like you said (getting on it when not warmed up). So thinking I might be lean I went up a size on the main and it did it worse. So I ended up going down a size from what was in there originally and it cleared up. I didn't do plug chop yet but I might be able to go down one more size.

Rupp250 · « **Reply #11 on:** May 07, 2014, 10:41:52 PM »

If it was blubbering from being rich I would go down more than 1 jet size. But do a proper plug chop when doing so.

pinned250r · « **Reply #12 on:** May 08, 2014, 10:40:40 PM »

Well a little update, i went down 2 sizes on the main, and did a run, it was super lean. Finally just decided im gonna do a compression check, and one gauge was only kicking 150, should be around 200. Buyin another gauge tomorrow. And tearing into top end if it shows low. I was also told to close my plug gap up with the stock ignition to .0018.

Jerry Hall · « **Reply #13 on:** May 09, 2014, 01:26:35 AM »

Quote from: pinned250r;33540

Well a little update, i went down 2 sizes on the main, and did a run, it was super lean. Finally just decided im gonna do a compression check, and one gauge was only kicking 150, should be around 200. Buyin another gauge tomorrow. And tearing into top end if it shows low. I was also told to close my plug gap up with the stock ignition to .0018.

I doubt if it would run with a plug gap of .0018" but .018" should run good and tell you if the misfire at 3/4 to full throttle is due to an ignition that is a little weak.

Disconnect and clean every plug in or plug together wire junction and into the CDI with compressed air and contact cleaner. You may need to crimp the female bullet connectors a little so that they will plug together tight. Disconnect the kill switch from the wiring harness.

Make sure your fuel is fresh and not what has been stored all winter in a gas can or in the fuel tank of the bike.

Check the spark plug cap resistance. If it has the OEM cap it should be about 5000 ohms +/- 1000 ohms. If you have not set the spark plug gap to .018" do it to a new spark plug and try it with the jet that has been making the engine blubber at wide open throttle and in the upper RPM range. If it blubbers with the new spark plug set to .018" plug gap, install the main jet that was two sizes smaller and test ride again.

If it misfires at wide open throttle just before it is time to shift and will run clean for a second or two each time you shifted a gear and then start to miss in each gear just before it is time to shift, the main jet is too rich. If the engine needed to be leaned down 2 jets to stop it from misfiring due to richness it IS NOT TOO LEAN NOW regardless of what you think you see reading the spark plug. If you only have a hand full of passes down the road at wide open throttle on a new spark plug, the spark plug at this point will look almost like a brand new spark plug. The porcelain will not have changed color any from that of a new spark plug and the silver or gold plating on the end of the steel shell will look brand new if you wipe it with a rag. The ground strap will have probably burned off most or all of the silver or gold plating. The end of the steel shell next to where the ground strap is attached may show some discoloration. If this is what your spark plug looks like you are probably still a couple of main jets away from the main jet that will make the best power.

pinned250r · « **Reply #14 on:** May 09, 2014, 09:04:51 AM »

Thanks for the great write up Jerry, i like that you cover ALL of the bases. I do have an OEM cap, i will check ohms on it.

This weekend is pretty ruined for working on the R as i had a strut break on my wifes car, and am master and and mistress of a wedding. But i will keep this updated.

Thanks guys