Illusion-Lighti

Here's my problem. I have a MRX 3 w/ a Picco G1 XP engine. I start the car and have it on top of my starter box to do the tuning. After I tune it to where I like it, i get it on the track. I gun it really good and the car responds very well for the first 5 seconds. Then after that it starts to pulse on and off. The power just keeps coming in pulses. If I completely let go of the throttle and let the car come to a stop it's nearly impossible for me to get the car moving again even though the engines still running. At this point I'll pull the throttle all the way down, but the engine just doesn't respond well, it seems to be able to get only to 20% throttle and the clutch won't engage so the car just sits there with a high idle when I'm pulling the throttle. What's really wierd is when I have the car on the start box doing the tunning I don't get this problem. Can someone tell me what's going on?

RC Dumb

think outside the box. So, have you checked your throttle servo?

Illusion-Lighti

Yea, the throttle servo works fine. It just seems to have the problem when the wheels have a load and only after like 5 seconds. if I let the car sit long enough, I'll be able to get good response again for another 5 seconds.

Would there be any chance that the clutch needs to be replaced? Heck, can the clutch even go bad with enough use?

GrandeGixxer

iTrader: (21)

it the engine pulsing? if it is the engine, it could be an air leak.

Illusion-Lighti

If there was an air leak, wouldn't it also perform inconsistent when the car was on the start box while i was tuning it?

SlobbaTech

Might be too lean and cutting out but not enough to stall the engine. There's been few times where I "thought" my engine was rich so I leaned it out then put it on the track and it was on lean side, so engine would have been tuned fine if dind't lean it out while sitting on the box.

whynot

iTrader: (18)

I would make sure that the clutch is set properly .Than I would back out the bottom end needle about 1 turn,Than see what happens. And if that doesnt help back out the top needle until it is noticably running rich and then slowly turn it in until it engauges the clutch and then put it on the track ad adjust to your liking.Hope this may help
mike

kidDynomite

I had this same problem recently. I swapped in a new motor for break-in, idled a couple tanks, put it on the track for low run-in, it went for a little bit then just sat ... stop n go etc ... I thought my tuning was off.

The problem was that I didn't add any shims on the SG shaft before putting the Tapered Collet. And therefore it wasn't really locked onto the flywheel.

So you may want to check your clutch assembly.

Good luck!

Illusion-Lighti

Yea I thought about it being my clutch too, but I've been running this car w/o adjusting any of that stuff for weeks now and it just recently started. The clutch wouldn't change its settings on its own would it?

kidDynomite

I-L, Anything can happen. Try spinning the flywheel with your fingers while the engine is cold. Let the piston stick with the compression. If it's really hard to move, your flywheel is probably on there pretty good. If it spins, it's not locked to the collet.

Illusion-Lighti

it's definitely locked pretty good. when i spin it, it'll stop when the piston hits the top. I need to apply a pretty good amount of force to get it to turn over.

gonzoY5

Try a different pipe and header. I had a guy here with a similar sounding problem. Motor would rev up then slowly start losing power. Once he let it sit for a bit, it would have power once again for abot 10 sec. He was using some old header/pipe witha wierd shape that wasn't letting the exhast flow out enough. Once he changed the header there was no problem. Good luck.

Illusion-Lighti

What I can't figure out is why this problem all of a sudden just happened. The car use to run perfectly and then just today. I spent 2 hrs tuning and finally just got tired of it.

HELLION

your clutch sounds like the problem to me ! check the thrust bearing and end play. Also sometimes servos can act up and will do strange things. Try putting your finger on the servo linkage (slightly loading it) as you give it some throttle (with the engine off) feel for any glitches. I helped a guy once that his car was pulsing. As I looked at it I noticed that he grabed the bellhousing with something that bent it while changing gears but you did say you havent messed with the clutch and thats why I think it's the thrust bearing . They don't last to long if they aren't greased often

whynot

iTrader: (18)

When it is on the starter box and you are reving it up can you feel if it is shifting into 2nd gear and does your motor sound tuned nice and crisp? If it does than it is your clutch when the weight of the car is against the clutch it is making it slip so when you are at a low rpm it is prob. grabing a little but when the motor really starts to sing a high rpm it isnt grabing the clutch bell enough.You need to add some shims so that your end play is just a little bit not real sloppy prob. about .3-.4 mm of end play and when you get that set you need to make sure that your clutch nut isnt to loose also if it isnt tight enough it can bog the motor down. so you prob. want the clutch to kick it atabout 1/4 of throttle but that is a personal preferance. Hope this helps.
mike