77 Cyclone 340 Lazy Mid Range Performance

[Liquifire 4/6]

I bought a 77 Cyclone 340 at a swap meet about 7 years ago and gave it to my brother to get him hooked on vintage sleds and it definitely got him interested in the hobby. He's ridden a couple vintage derbies on it every year since he got it. However, it has been extremely lazy in it's mid range power since we acquired it. In the first year, I cleaned the carb and installed a new needle/seat assembly as well as changed all the fuel lines. Two years ago, I rebuilt the clutches with new bushings and the correct new flyweights in the primary and new buttons in the driven unit. I had hoped that would make a huge difference because the original bushings and weights were pretty sloppy. Unfortunately, it still is quite a dog from 5 mph - 40 mph and I am looking for some opinions on what you guys think might be ailing it?

It always starts great and always runs on both cylinders. It seems perform ok at the very bottom end as in engagement to about 5-10 mph. Then it gets into it's unimpressive mode and you feel like you are never going to get any top speed out of it. But on hard pack, it will eventually wind out sometimes taking 1/2 mile to get up to around 35 mph or so. Then, once you get past the 40 mph mark, it really hauls the mail and you'd swear it was a 440 not a 340. It'll hit an easy 60 mph on a good trail but just don't slow down below 35 mph with it or your buddies will be way ahead before you get up to speed again.

I should mention that I took the engine apart yesterday to reseal it. I thought that by disassembling the engine, I might notice something amiss that might be causing the problem but I can't say I really saw anything terribly wrong. The outer seals did seem rather loose on the crank yet I saw virtually no evidence of leakage past either the PTO or Mag end seal. The pistons looked in beautiful condition as did the rings. I did replace the rings but only because I happed to have a few NOS rings sets kicking around. And for kicks, I replaced the trigger assembly (behind the stator) and again I did so only because I had an NOS trigger sitting on the shelf. The reed petals look in great condition and the cylinder walls still seemed to have some signs of a cross hatch pattern left on them.
I was a bit disappointed to find that JD used conventional seals for the center seals but at least there are two of them. The center seals did seem a tad sloppy on the shaft however they were still a much nicer fit around the shaft than were the outer seals. And seeing that the outer seals did not seem to be leaking, I want to assume the center seals should still be ok?

I'll have the sled back together next week but the snow is gone now so I won't really know if it's going to perform any better until next winter. Do any of you guys have some suggestions on what could be making the sled so pathetic in the mid range department? Thanks!

[WinnipegStPaul9]

Peter, don't have an answer but wanted to tell you it's good to see you back here.


DA

[skoalmint]

Might be a weak secondary spring ! I had one with the same symptoms , Basically the spring gets weak, allows the secondary to shift to a higher ratio before the engine can get the rpms up enough to sustain the load.I didnt have a new spring at the time so i just moved the spring up one hole in the helix, helped the machine greatly ! Just my opinion I am probably wrong as usual LOL.Hope this helps . Brock

[JDT]

I like Brock's idea also. Wouldn't hurt to give it a try.

[Liquifire 4/6]

Thanks a bunch for the suggestion on the weak secondary spring, fellows. That does make sense that the sled might behave the way it does if the spring is sacked out. I have the engine here at my shop but the rest of the sled is at my brothers place so when I visit him this weekend, I'll take a peek at the driven clutch.

And thanks DA, for the warm welcome back. I guess I haven't posted much in here for the last couple years, but I have been reading the posts now and then. I've been pretty busy for the last while with work and other (non JD) sleds that I haven't had the time to get on the forum that much. But the John Deeres have always been my favourite sleds and I'll be playing around with a couple of them this summer. I have a Snowfire and a 340 Trailfire that are in great shape however I haven't ran them much for a few seasons because I've been worried about the crank seal condition in both of them. So I have new gaskets sets ordered for both of them and will be resealing them this summers so I can enjoy putting some miles on them next winter.

[MARK S]

There was a service bulletin on those back in the day.We changed ALOT of them over.The main jet and pilot jet were both replaced with smaller ones..If I remember right the main was huge like 400 and the pilot was?? I would have to do some digging in my notes but I think we put in a 300 main and 25?? pilot..then test drove it to check sparkplug color..They realy ran nice after that, Mark.

[Liquifire 4/6]

I finally had a chance to take a peek at the secondary clutch. The spring tension seems ok although I did not have a scale handy to get an accurate reading on it. But I think I may have found the problem. The main bushing in the driven clutch seems to have way to much sloppiness. With the helix removed, you can really wiggle the sheave around quite a bit. The bushing inside the helix is also worn to some degree but I think it's still good enough to run. Any ideas where a person might find the bushing that fits inside the stationary sheave of the driven clutch? I checked ebay and New Breed but to no avail.