it seems i have a tuning problem.

[kryptonite]

so ya. ive come to realize my tt may have a tuning issue. its easer to just show a vid, then going back and forth. i always thought this was a symptom of being over geared, but today, for giggles i swapt back to stock gearing just to see. and it does the same thing. i thought it might be too rich and loading up, so i leaned it out, but it did nothing. maybe becouse it was? i don't really know why, but now i want to fix it. my mt on-road is over geared and it is consistantly the same for the whole tank. also take note to the difrence in the pipe sound. in the beginning it crackles, then it gets muffled and soft. i normally run 31/29 gears, but today went back to stock 29/31. the motor is an o'bros ported 26.9 with a stock carb and 8k spring. it did this before the motor job as well.


http://www.hobbyzip.com/videos/947/my-tuning-issue.html

 

[varga1974]

I have noticed with my engines as well that you loose power as they completely warm up. What I noticed that works well for me if my low end is actually a little bit rich so it stumples alittle before it warms up. As the engine warms up if will run leaner causing your power in the low end to drop. I hope that helps you out some, and maybe some of the other guys have some ideas for you.


Steve

 

[DemonRC]

I'd try tuning it warm. I bet it's running lean. When it's warm let it sit for a minute at idle to build up fuel on the plug then do a WOT run and immediatly shut it off to burn the deposits off the plug. Then check the color of it. I bet it's grey.

 

[kryptonite]

ok, so i pulled the head today to check for leaks. im am using the blue gaskit, but its fine. no blow thru or anything. cleaned the carb and jets out. it look ok, but i cant be sure. the plug is always fine. light brown. i fired it up, let it warm in and checked for leaks around the seales and the seemed to be fine. ive had leaks before, but it would run diffrent. this idles fine and runs smooth. doesn't stumble at the top or anything. it just sounds funny and is really slugish of the line when it gets warmed up. i set my carb back to stock. it ran like crap and barely wont idle. im going to re0tune it today with the gears i normally run and see what happens. i forgot to take note to where the needles where before pulling them out, so i guess i'll never know


does anybody think it could be the ring losing compression? im unsure how much time is on it, but this new head probly only has 1.5 to 2 gallons. the thing is that it did this before the new mill. sometimes its worse then others, but i just don't notice becouse its always WOT. going for a test-n-tune.

 

[IMADMAN]

Clutch?


Yea, check the clutch it may be engaging to early, or the spring looses it's tension rating after getting warmed up or hot. If you have a spare ring I would also change it out if you have the head apart.

 

[kryptonite]

so i just got back.. its a mess. i started tuning it on the dirt road. had it tuned in about 15 minutes. took it on the grass and in a few laps it started bogging down. pulled it over and let it sit at idle for about 8 minutes.(got mt started for wifey).. put it back on the grass and it was an animal.. 5 minutes later its back to square one.. bogging down, so i did some speed runs(still dragging ass) on the dirt road to check the plug and its fine. light brown.. so i leaned it out. went a little better, but a few laps in she wont go till the pipe kicks on. checked plug, its white(i leaned it out). so i swapt gears. back to the 29/31. cleaned plug and retuned really quick, again, animal off the line, but coming out of the turn it sounded like the clutch slipping. hard to tell couse my tires arent that good. but within a few minutes it started again. bogging and dragging ass till the pipe kicked on. most of the time its still drivable, but now it cant even get out of its own way. i sprayed the whole thing down with wd-40 and the motor didnt spike. its hard to get to the main seals. but i really don't think an air leak couses this. its not running lean and keeps an idle.


MOO-IMAD the clutch is something to look at. its the only thing that has stayed the same. it doesn't feel like anything is dragging. i would think if the spring gets hot and lose that the motor will still pick up. i didnt think to rev the motor to see where its grabbing. i keep looking at the tune becouse of how the pipe sounds muffled when it gets warmed up. when i pulled the head it all looked good. nice and clean and the ring looked fresh, but im still going to order a new ring, or simply blow this motor up and start over. i just really want to figure this out first


on the lighter side. still had enough fun to break a drive cup,drive shaft, stearing servo, and a stearing mount, and the wifey ran a full tank thru the MT. she said that is now hers and she loves it. she giggled like a school girl when she realized that if she runs over my truggy it makes a cool jump. she was way too cute out there with here manicured nails and a mini skirt..

 

[IMADMAN]

Yea I would throw in a clutch assm. or spring if you got any of those on hand. I had a similar problem- With the wheels off the ground it would rev to the moon! as soon as I put it on the ground and it would just bog and die, I tried adj. the Hi -needle from 2.75 out to 1-7/8. The L- needle from 1.75-7/8 and it would'nt make a difference. I changed the spring-Bingo! problem solved. I'm guess your spring may have lost it's tension rating, or possibly broken? It seem that after 20mins. the clutch engages but it does'nt have the brute power like it has when it's cold.

 

[kryptonite]

Yea I would throw in a clutch assm. or spring if you got any of those on hand. I had a similar problem- With the wheels off the ground it would rev to the moon! as soon as I put it on the ground and it would just bog and die, I tried adj. the Hi -needle from 2.75 out to 1-7/8. The L- needle from 1.75-7/8 and it would'nt make a difference. I changed the spring-Bingo! problem solved. I'm guess your spring may have lost it's tension rating, or possibly broken? It seem that after 20mins. the clutch engages but it does'nt have the brute power like it has when it's cold.

ya imad. im going thru my MANY unedited vids and looking at this and it seems to progressivly get worse( i record all my session). i can see it widdle away on each session, but it wasnt enough to really notice it. by tonight i will have it apart(AGAIN) and check out the clutch and replace it with a new one, but im going to use the stock spring. i'll check it out in the morning and see how it goes..

 

[Clubin]

I had a simular issue, turnsout the bearing on the clutch side was real loose, it looks like that bearing wasn't getting any lubrication!. I installed new bearings and seals, and everything is perfect again. How much fuel do you figure you have through it? This was the engine in my MT and there was probaly 2 gallons through it.


Or you might want to install a new ring, when you had the cylinder off did you check the wear on the ring?

 

[kryptonite]

hey clubin. your talkin bout case bearings? the case has about 4 gallons total, maybe more. im thinking the top end has a little more then a gallon. i started to notice this problem at about the one gallon mark, shortly after installing the pipe, then i started running 31/29 gears too so it kind of made sence then that it would drag a little. i checked the top end last night and it really looked new. little to no signs of wear. so the case bearing? you mean yours was siezed or sucking air? i have the new stock case bearings that came out of my on-road mt, but no "new" seals. i really don't want to take the mill apart again. im going to try my new clutch first as thats easy. if that don't work then im going for the case bearings. i know they don't last long. i also really want to see wich one it could be. the clutch is a possibility, but it just feels like a motor problem..


thanx clubin. i pretty much counted that out couse i don't think its pulling air, but now that i think about it, it could very well be that.

 

[Clubin]

When you are changing the clutch shoes see if there is any up/down play on the crank shaft - the case bearing on that side is the one that failed for me.


It wasn't seized, the seal did not appear to have failed, the bearing looked like it ran dry? The bearing was very badly worn, and lots of black fine shavings migrated through the engine. Some how the top end survived and is still running strong.


Stock cy bearings do suck, but this is the first time I have seen one fail.

 

[hamster huey]

don't laugh at me but I had the same symptoms and it was a dirty air filter. I always start with the stock 1.5,1.25 and only go 2 hours on either. If I have to go any more I stop right there and clean the filter before I assume the problem is somthing else. don't laugh again at this one but the spark plugs do unscrew themselves over time also but usually mine wont even start if that happens. In an article in the july 09 r/c car mag Oneill brothers racing states the average piston ring will last about 20 hours of run time and usually after 2 piston rings have been changed its time for a full set of gaskets and bearings. Some things to consider among many.

 

[kryptonite]

MOO-just watched your vid and here the low end lag that refer too. mine used to be like that, but has now gottin really bad. do you think thats the clutch?

 

[IMADMAN]

I would think that if it runs great for 15-20 mins, then the performance goes to crap, I would'nt think it's an eng. or tuning issue either. Like you said earlier the clutch is the only thing that did'nt change. So that's where I would suspect the issue lies.

 

[max 1]

I Just Had The Same Thing Hapen To Me Last Week ,i Tore The Hole Thing Apart Chect Every Thing .i Thot Look Real Close At The Cyl ,and Fond Crathes In It Athe Top ,leting Blow By,my Aie Cleaner Lid Fell Of A Couple Of Tims ,and I Did,t Think About It,put And Old Head Kit On It And Was Fine .drove Me Nuts Trying To Find The Prob ,i Post,d It Last Week Befor I Took 4 Days Of .so Put A Ported 30.5 In ,now I,am Going To Break Somthing ,or Break It In.it Woud Not Even Move ,sat There And Ideld Just Fine ,would Not Even Reve Past Idle.

 

[hamster huey]

My throttle shaft also wore out and did something similar to that.

 

[kryptonite]

i think it was the clutch spring. i replaced it with a stock spring. i ran it for a little bit and it stayed the same till it ran out of gas. i havent run it since then, but im thinking it is ok now. i just need to get out and run it hard for a full tank and see how it does.