Need some engine help

[o4twinpeaks]

2008 apex

wiring harness bypassed

We were running last week and I thought I heard him breaking down on the take off.(we do dirt drags) Was running fine on all but the last 2 passes. Got to work on it today before our race and can't seem to get it running right. Anything above 7500 rpm and it runs fine. It's breaking up and just sounds real "labored" to gain rpms. New plug. Noticed cap was a little loose so new wire and cap went on today. Cleaned carb. 28mm keihin round slide. 128 main 38 pilot needle lowest position(c clip in top notch) 1 1/2 turns out on air screw. When I disassembled the carb noticed alot of wear on the slide to the point were the chrome coating is coming off in some spots. Also the ramp on the slide where the idle screw sits has some bad marks in it. Idle screw is turned in till spring is fully compressed and idle is at 1500. Inline fuel filter and fuel line new as of today. Wide open reading on plug is a light chocolate color. It seems to be loading up and running too rich on bottom end. I personally think carb is gone and a new one will be ordered on monday. Could I be dealing with electrical problem? Would think it would break down on top end with electrical issues. Not clutching as it dose it on the stand also. Turning 10500 on the track just as it has all year. I saw 12000 on the stand but I attribute that to a loose plug cap. most I have ever seen on the stand before is 10900.

I haven checked the reeds yet because I didn't have any with me today or new gaskets either. I will be heading out to harbor freight in the am to pick up compression tester. I feel the compression is still good but the numbers wont lie.

What else should I look for?

Is it worth going to the power jet carb? Looking at a stage 6.

If this ends up being ignition Is it worth going to a pvl?

We run in the modified classes so anything goes as long as we hold it to under 120cc and still runs on race gas.

[LT80]

Crank seals?

[mmsoup]

Before you spend money throwing parts at it, maybe think about dropping the clip on the needle. Sounds awful lean to me. Go to middle position or one position below middle in steps and see if you have an improvement.
We were chasing a low-end bog on another kids race quad at the PA GNCC and it was acting like it was loading up and then would finally hit.

He had:

Justins reverse Haggerty
2Fast Pipe
Malossi Cylinder
PVL ignition
Stage 6 28 mm carb

He had the needle second from the top and we moved it down to second from bottom and things improved. His son was able to race.
Subsequently he bought a Keihin Airstriker 28 (D Slide) and reports issue totally resolved. I would check that first

Another issue that can act like that is a bad/weak torque spring, is yours new or different or has something change or has it been there too long?

Also check the clutch shoe springs to make sure you aren't dragging a shoe

For what it's worth, we run the Keihin 28mm D Slide in both of our bikes and wouldn't have anything else. Had a Stage 6 28 powerjet and had issues with it. I have heard that the needle is an issue in that carb but would suggest you contact Justin at Max RPM for specifics.
We also run Stage 6 PVL's with really good results.



Hope that helps

[selbygirl]

zip tie the plug wire to the spark plug .. is it a cvt .if it is maybe a weak spring . check for air leaks around intake . spray carb cleaner when running see if rpms rise or lower . i would use a pvl . and maybe do a leak down test. i think you you can make one for about 30 bucks.. like lt 80 sed sounds like crankseals.since you lowerd your clip to bottom

[o4twinpeaks]

Ok I forgot to mention the needle is lowered all the way to lean it out(clip in top position ). Plug is dripping wet with fuel when doing a plug reading at 5500 rpm. Literally fuel dripping off the plug when i removed it to do the compression test. Did compression test on it this morning and was only getting 100. This was after the bike was warmed up and 10 good kicks with throttle wide open. I picked up a leak down tester today also but I need to come up with some plugs for the exhaust and intake. will do that this week. Had to do the fathers day thing today so only had about an hour to work on it. I pulled the reed block and the petals look to be in good shape but on both sides are about .003" from sealing completely. Not sure if this is the way it supposed to be or not. I imagine that as soon as the cases start to be pressurized they push back and seal but not sure. Took some picks and will try to get them on here from my phone in a few.

With the suggestion towards torque springs this is breaking down before the clutch even hits. Stall is right at 6000 plus if I'm running on the stand with the tires in the air that takes the clutch out of the equation. Am I wrong on this? Should I pull the belt? Do I pull the rollers out to run without the belt? I'd pull the whole clutch off but then there's no way to start it.

I'm still leaning towards carb issues. The needle is so worn on the top clip grove that the eclip will almost fall off. That grove is almost 2 times as wide from the wear.

With compression being down Looks like its time for a top end job also. I would prefer to get this breaking down issue solved before doing the top end but I might just have to do it all at once. I hope I can get through the rest of this season with just doing rings and piston because we were budgeting for a big motor for next year.

[o4twinpeaks]

pic of reed gap

[mmsoup]

Damn I love chasing these little Gremlins............

Could very well just be the carb, do you have a spare or a loaner you can throw on to check?

Also, 100 pounds sounds pretty soft.

We made our own leak down test kit and we use a freeze plug to seal off the exhaust.

If you've never done before, take it up to 6 lbs and it should hold for 10 minutes with no loss.

Good luck tell us what it was

[selbygirl]

try the clip lower .. reeds shouldnt have a gap no wider then the thickness of a nickel , but i had them wider and still ran good . plus you can flip your reeds. the compresion seems low. is it hard to start. when i do a compresion check. i hold the gas wide open and kick untill the needle on compresion checker wont move enymore... just a couple of weeks ago i had a bike act funny like it was the carb . it was one of the shoe springs went bad. check your variator .. see if it moves freely in hand. we run the over range set up .after every moto i clean mine with a rag .for some reason the over range set up seems real sensitive .. but sounds kinda low on compresion .. maybe a new piston ring

[o4twinpeaks]

Originally posted by selbygirl
try the clip lower .. reeds shouldnt have a gap no wider then the thickness of a nickel , but i had them wider and still ran good . plus you can flip your reeds. the compresion seems low. is it hard to start. when i do a compresion check. i hold the gas wide open and kick untill the needle on compresion checker wont move enymore... just a couple of weeks ago i had a bike act funny like it was the carb . it was one of the shoe springs went bad. check your variator .. see if it moves freely in hand. we run the over range set up .after every moto i clean mine with a rag .for some reason the over range set up seems real sensitive .. but sounds kinda low on compresion .. maybe a new piston ring

We are running the mallossi overange also. Will check it out. Bike always starts on 1st or second kick for me. Joey hasn't got the hang of the kicker yet.
Well I have a gap about the thickness of a piece of notebook paper. .003" See I do remember something from my machime shop days over 20 yrs ago. Now its all done on computer. Only good carbs I have are 20mm. I do have 2 oko 28 and a 30 laying in a box of parts I got but Know nothing about them and don't trust them. If the stage 6's are giving some trouble I'll just go with the pwk.

Almost called you today but didn't want to bother you on fathers day. We were out shooting and swimming most of the day.

Tom Petrick

[selbygirl]

you could of called .. we where getting every thing ready for this wednesday .we are heading to dublin gap mx there having moto cross for christ camp .. its from wed to saterday . they teach the kids rideing skills . and they have mechanics there .. and other activitys for the kids and a band and its free .. but you have to sighn up for it way in advance .. you guys should check out there web sight www.motocrossforchrist.com

[JIM GRACE]

Try lowering the pilot jet, that will lean out the low end. IMO

[jerkyboy]

The low compresion could be your whole problem.

[o4twinpeaks]

All issues will be fixed!!! lol

I pulled it down today after work and looks like my squish was a little tight. I have no rod play but can see a mark on the head where the piston was just starting to kiss. I mic'd the base gaskets that were on there and came up with .029 on one and .024 on the other. Looks like I will be looking for a few of the larger ones and some squish test when putting it back together. Carb slide is so worn and loose in the bore its done. Not sure if im going with a koso or stage 6 yet. Thinking about bumping up to a 30 in prep for big bore this winter. Going to hold off on a pvl for right now unless I run into a killer deal.

[o4twinpeaks]

Update

Up and running. New top end v force reeds 30mm koso and trackside pipe. Started with a 40 pilot jet 138 main 1 1/2 on the air screw and needle in middle position. Still a little rich on bottom end but running ok to do heat cycles and break in the top end. Few more heat cycles then off to hetricks dyno fri am to get malossi pvl on and tuned in.

[o4twinpeaks]

Well did bearings and seals and tuned in yesterday. I dont think the seals were leaking yet but when we went to install the pvl we felt some play in the crank. We ran the bike on the dyno and all was well then ended up doing the bearings and seals and still made the exact same #'s. We just gained 4 hp at the hole shot with the pvl. Jetting ended up being spot on as did the clutching.

[selbygirl]

hay tom after you put your new crank bearings in did you still have play in your crank or did the new bearing make it tighter.... and how many horses did the dyno show .. just curious take care tommy

[o4twinpeaks]

I really didn't check it after. LOL I should have. I was more concerned with learning how to set up the pvl and getting the squish right.
Actually peak hp was before the pvl. 16.66