Low RPMs in a '96 670

[elsmack]

Can you guys give some possible causes for my stock '96 Summit 670 only getting up to 7200-ish RPM under load? Under no load it revs to 8400 easily. My HAC was replaced last season after it failed. I have had the primary and secondary clutches looked at by a good local shop, they said they looked fine wear wise, and the setup was correct for this altitude (4500, SLC Utah). The clickers are on 6, putting them back in the middle setting drops me about 400 RPM at WOT. I don't remember the compression numbers but the shop OK'd that too.

The sled had 4800 miles on it and I ride like an old man, so it hasn't been pounded much. I have owned it since 98 and only put 1200 miles on it. Motor pulls well down low, but gets anemic and wont get over 7200.

I'm going to change the bearings on the jackshaft and look for wear down the rest of the driveline, I think it's time for that. Belt is correct for the sled and new last year.

What else should I look for, after I pull and clean the carbs?

 

[Skidoohmx]

Make sure and check that the rave valves are functioning properly. Check to make sure they slide in and out and are not gummed up.

 

[elsmack]

Thanks, Skidoohmx. I have never cleaned my RAVE valves, and had never given them a second thought till now. It doesn't look like a difficult job, judging from a couple how-to guides on the web.

Any other thoughts anyone has is very much appreciated.

 

[winter brew]

Did they put new springs in both clutches?? might be the correct springs but they do sack out over time.

 

[elsmack]

I am not sure if they changed springs. Whatever they did helped some, but I don't remember the details. I do remember that they changed out several wear parts, so maybe they did the springs too. I will call and see if they still have the service record from last year. Before the shop visit I was only hitting 6800, they got me up to 7200 and there was a very noticeable improvement on how it pulled down low.

Now if I clean my RAVE valves and get my top end back, I might have something. If the RAVEs are stuck closed, it would match my symptoms of weak top end and low RPM, but it still pulls well off idle.

Thanks, Winter Brew.

 

[eazyduzit509]

Clean them RAVE's once a year and yer golden.

 

[banditpowdercoat]

Spring's are tired in the clutches. Raves might be dirty as well, but I'll put money on tired springs. Primary spring should be changed every 1000 miles for best operation.

 

[d&mraceengines]

clutch springs and belt are probably the problems 1000 miles on a belt is alot of miles i wish i could get 500 out of a belt
my .02cents good luck
dan

 

[sledsrock]

clutch springs and belt are probably the problems 1000 miles on a belt is alot of miles i wish i could get 500 out of a belt
my .02cents good luck
dan

As most people have stated, Rave's and/or Clutch springs most likely the culprit. Doubt the belt, but maybe........and 1000 miles for a belt is not really alot. If your only getting 500, something is wrong.......wrong belt, not geared properly, not clutched properly.

 

[elsmack]

Thanks for the input BanditPC, D&M, and Summit670. I appreciate it.

I talked to the shop and they did not change the springs, so I am going to do that and clean the RAVEs. Another thread also suggested lowering the gear ratio and adding some pin weight to the clutch fingers as cheap performance increase, so I am going to do that too, after I get the old girl running properly. I don't want to mask problems with mods.

 

[banditpowdercoat]

Lowering gear ratio will help accelerate, and power, at possible expense of top speed. i say Possible, because most sleds are over geared from factory.

But, adding pinweight to the clutch will make RPM even LOWER. best to get everyting working right, then see what you need yes. Read up on Clutching IQ here http://www.mxzx-revzone.com/ to help understand a little more what does what in the clutches.