Cutting out at 30 mph?

fulltilt · Post by **fulltilt** » Sat Jun 17, 2006 2:07 pm

So I went nuts on this thing last night. First I did the pulley mod. I drilled a hole in the rear baffle of the muffler through the tailpipe, but that didn't do anything. Then I did the torch trick on the spare muffler I had. I was amazed that I did it without destroying the muffler. Much louder but much better. You can definitely hear a difference between the two when you tap them. One sounds hollow and one sounds solid. I was now up 4 mph to 32 or 33. I scrounged around and found a K&N that I had and put it on, and I think I finally understood what the lean surging was. I took a jet and enlarged it. The smallest drill bit I had was .039". I did some funny stuff to make a half step first, not sure exactly what size, but it still surged. So I went the full .039", or a 99 jet. Now it pulled real strong up to 30, but then it cut out real bad. So I put on the stock airbox to rule out the K&N. It ran bad. Took off the airbox lid and more power again, back up to 30, but it's still cutting out. Any ideas?

fulltilt · Post by **fulltilt** » Sat Jun 17, 2006 2:08 pm

Oh, by the way it's a 1985 Spree.

MySpree · Post by **MySpree** » Sat Jun 17, 2006 2:21 pm

its cuz u drilled out ur main jet.

fulltilt · Post by **fulltilt** » Sat Jun 17, 2006 3:11 pm

But why would it pull so hard up to thirty, wouldn't that say I'm clearly on the main jet and the air fuel mixture is right?

MySpree · Post by **MySpree** » Sat Jun 17, 2006 4:30 pm

well if u drilled out the main jet and it slowed down, and then u put it back stock but kept the main jet i see thats the problem.

darat · Post by **darat** » Sat Jun 17, 2006 8:51 pm

y would u drill it out.

fulltilt · Post by **fulltilt** » Sun Jun 18, 2006 12:47 pm

To get more fuel.

Post by **noiseguy** » Sun Jun 18, 2006 12:55 pm

I think you're probably running a bit rich. Typically guys are running 90 jets with K&N's. But at least it's running. How is it cutting out? Do you have good fuel flow from the tank under vacuum? A plugged filter could be starving the bowl.

Have you ported out the intake? I'm wondering if it's having breathing problems at the higher RPMs.

fulltilt · Post by **fulltilt** » Mon Jun 19, 2006 8:50 am

Yup, I ported the intake. It cuts out like it's a rev limiter. Like maybe spark? It seems like if it were rich it wouldn't get me as far as it does without running bad. I want to build an expansion chamber, as it would be real easy with my TIG welder, but I'm not yet happy with that design program. Seems like every time I change something, the OD changes, and it doesn't have a place to change displacement. Looks like you're thinking of building one. Can you confirm what OD and overall length you have decided on?

Post by **noiseguy** » Mon Jun 19, 2006 9:21 am

There's no spark rev limiter on these. It'll run as fast as you can get it to flow.

I went through the whole design iteration thing with a few different formulas. If you design around the Spree's tiny porting, you end up with basically a straight pipe. There's a link to a program in Adv Tech Docs.

What I ended up doing instead was buying Chinese pocketbike expansion chambers and modifying them. This saves a lot of bending time and having to construct a silencer. If you read up in the performance section there's a post with pictures of what it looks like. The pipe I used is tuned for around 9-10K, and the design seems to follow the correct basic principals. The packaging is a bit tricky; buy two and play with cardboard first. I use a stock downpipe as a donor, as rusted Spree mufflers are plentiful. If you do all this and can weld, it's an afternoon project.

fulltilt · Post by **fulltilt** » Mon Jun 19, 2006 12:00 pm

It just acts like a rev limiter. Could be a fuel supply issue I guess. It's a new filter though. I saw your exhaust, but you wrote recently that you were going to start building expansion chambers, I figured that meant building one from scratch. I'd weld one up from a pocket bike in a second if I could find one cheap, but I can't seem to find any on Ebay right now. I need to mill my head too. Why did you only go .015?

Post by **noiseguy** » Mon Jun 19, 2006 8:13 pm

.017" as I recall was where the machinist ended up. .020" is the thickness of the head gasket, which the engine will run without. You can use lead solder to check your static clearance overall; I've heard of guys running 50cc's down to .010" clearance but wouldn't personally try it. You'll be happy with the performance improvement.

fulltilt · Post by **fulltilt** » Tue Jun 20, 2006 8:02 am

I was wondering about that. I think I'l try running it wiithout first. I've got a 68 jet coming too. I need clutch springs pretty bad. They are kind of a pain to buy, as they don't have any distributors in the states. That should help my low rpm clutch chatter that showed up after the pulley mod.

darat · Post by **darat** » Tue Jun 20, 2006 1:59 pm

u can get the springs thro top speed or some thing like that were talking about it awhile ago.

fulltilt · Post by **fulltilt** » Tue Jun 20, 2006 10:53 pm

Searched the forum, couldn't find anything about Top Speed. Anyone know how to contact them?