I sold my 88 mojave to my buddy but i still work on it all the time. When i bought it, I replaced the head, valves, springs, cam chain, cam chain tensioner, seats, cams, and everything else in the top end. We are having a problem keeping the valves adjusted. It runs great after you adjust the clearance and fires up on the first kick. After we run it for about 20 minutes it will not start unless you choke it and give it full throttle. I take the head off and the valves have no clearance, they are completely tight again. What would cause this? Is it the valve seats going out? Are the valves getting sucked into the head? This happened before and i had to replace the head. Are there better spings and valves that we could buy to prevent this? Thanks for the help.

 

I have heard of the valves sucking into the head on Mojaves. I have three Mojaves and have never had it happen. I used SS valves from FST on one build, but then changed to the Vesrah stock replacements when I built the next one. No problems with either one. I set the intakes at .008" and the exhaust at .010". I also have worn out two stock mojave engines before building them and never had the problem on them either. See if you can rig up something to measure the height of the valve in relation to the head and then remeasure after it tightens again. This should let you know if it is sucking the valve into the head. Good luck and post the problem once you discover it.

 

Mojaveaddict, thanks for the help. When i first bought the bike it did suck the valves into the head. So i replaced everything. It was very expensive so we don't want to have to do it again. I replaced the valves with the stock ones. Maybe we should try those brands mentioned by you. Where can we buy these? How much do they run? I hope it isn't too late to try to change them so we don't have to buy a new head. Thanks for the help.

 

You can buy stainless steel valves from Four Stroke Tech or Powroll for about 35 bucks each. The best place to buy stock kawi parts and some other stuff that I have found is Midwest Action Cycle. They give good discounts on stock parts. I bought the Vesrah brand replacement valves from MAC for about 12 or 15 dollars i think. I have ran the SS and Vesrah with stronger high rev springs and still had no problems.

I don't have the phone numbers for these places handy right now, but they all advertise in the mags and MAC and Powroll have web sites. If you can't find the numbers, post again and I will get them for you.

I wonder what is causing you to have this problem? Does the motor seem to run hot? Is the mixture lean causing overheated valves? I would look closely at the spark plug for signs of electrode pitting or melting. Many people run stronger springs on stock valves without problems, there must be a root cause for this. Mickey dunlap at FST told me that he always used the stainless valves because the stock ones would suck in. But then when he was building the Kawi XC racer they had him use stock valves and he said he never had a problem with them. The Vesrah valves are thicker than the stock ones and look stronger but they appear to not flow as well because of the thicker size. I used them anyway in a head that i ported and the motor has no rev limiter. I often rev it untill the valves float and cause it to skip. It has high rev springs and this happens at a very high rpm. Even so, no valve problems.

Good luck, keep me posted.

 

Thanks for getting back to me so fast mojaveaddict. You must be reading all the other posts right now as i am. Do you think that the stainless steel valves are much better than the vesrah ones? Is it worth it to spend the extra money? I know that it is sucking the valves into the head. It did the same thing before. I set the valves at the same specs you do. I run the bike for 20 minutes or so then shut it off and it won't kick start. Then pull the head off and the valves have no clearance at all. I hope that it isn't too late to put different valves in there. I will keep you posted. Thanks again for the help.

 

Nope, i had the same problem about 4 months ago i had to keep adjust the valves cause they were getting to tight and i took it to the shop and i needed new valve seats now it runs great and havent had to adjust the valves yet. try the valve seats they arent ver expensive and could be a quick fix. You may want to check the valves too because they may be worn and not opening and closing properly.

 

meangreenmachine, You said you replaced the head. If it was a new head it would have had new valve seats in it. was it new or used and how long ago in riding time has it been? On my two engine builds, one on an 89 with tons of riding time and one on a 94 I bought used, the valve seats were worn a little. I just cut a new three angle seat on them and installed the new valves, never have replaced the seats on three engine builds to this point. Since yours is an 88 and mojave87 must have an 87, I wonder if the early models had seats of a different quality material.

As for the stainless question, the answer is no. that is why I switched to the much less expensive Vesrah valves.

Good luck