Alright guys, I hope someone can shed some light on this issue because I am completely out of ideas. So I recently rebuilt my 91 kq 300. After all the break in I did, which is about 200 or so miles of hard accelerating and deceleration, I raised the compression from 90 to 150. But I just don't have any low end torque. The top end works great but when I'm pulling something in 1st gear the power isn't there. I have gone through the carb cleaned it several times and replaced some parts that were clearly bad, ie the vacuum diaphragm. When i cleaned it i set the idle screw back to stock (2 Turns out). After this i started adjusting the screw trying to find the solution. It seems like no matter where i put the screw the plug always tells me I'm running way rich.Today i cleaned the plug reset the screw to stock and it seems better. I let it idle for about 5 or 6 minutes and the plug was already beginning to get black. Also if i let it idle then stand on the throttle it sputters before it wraps up. I'm at a complete loss on what to do.

Carb Specs:
Main Jet: 112 (Set For 6000 ft)
Jet Needle Clip: 4th Groove (Stock)
Pilot Jet: 40 (Stock)
Screw Opening: 2
Float level: 13mm.

 

Are you sure the cam timing is right? And the valve lash? Do you have the air box lid on and all that stuff like it was from the factory?

The regulators are bad on those quads so checking the voltage while it's running may be a good thing. It shouldn't be higher than 14.4 or so. When mine spikes up to 17 or 18, it runs crappy like a plugged carb. Turning the lights on usually helps.

But I'm betting your cam timing is off or there is some problem there with the valves.

 

The air box and everything is set up exactly like factory. Yesterday to try and rule out the valves i opened the air box while it was running (only at idle) and there wasn't any pressure coming back up the intake. however it did backfire up the carb once and it has been being hard to start so i can check that again this weekend. Ill check the regulator tonight and see where that is. So if it is the cam being off another tooth then when i take that apart Im wondering if i should replace the chain because its at 7,000 miles and never been changed so its pretty loose.

Just a note on starting, the machine starts fine when its warm but when its cold it will try and start but wont unless i pin the throttle open for a few cranks.

 

Hard starting when cold is a sign the intake valve isn't closing all the way and your lash is too tight. Once you get the rpms up, there isn't enough time for the compression gases to leak around the valve, but at low rpms or when starting, the gases leak and there is your lack of low-end grunt. You may have a junk intake valve. Loosen the lash on the intake and see if that fixes it.

 

Ok. I will check the lash on the intake side. As far as I know the valve shoukdnt leak because before I reassembled I lapped them and checked for leaks with air conpressor and couldnt find any. I checked the regulator this morning and it looks good so its either the lash or the timing. How difficult is it to change out that cam chain?

 

You probably shouldn't have lapped them. It grinds the hardness off the valve. Intake valves are touchy. I rebuilt mine and put in a new valve, but it didn't make it a year before I had to start backing the lash off every few months. I'm thinking of buying a seat-cutter so I can match the seat exactly to the valve face. I think that is the problem with all the machines.

I can't imagine you need a new chain because it's so beefy. I bought a new one, which was really hard to find actually, and when the new one arrived, it was only a hair shorter than the one I thought may have been stretched. It's a pain to change as well. You have to buy a flywheel puller and beat n bang for hours and use torches and hope n pray. It just isn't worth it unless you know for sure you need one (unlikely).

 

I did not know that about the valves. That picture you posted is what the original intake looked like when i did the initial tear down. So I guess I will have to think about getting a new one. Im not reall shure what to do with the cam chain now. My tensioner is all the way out and i can rotate the cam about a tooth before it tightens. It also has some marks inside the valve cover. That is a little dissapointing now knowing that i basically set myself up for it to fail by lapping it. Ill take a look at the lash hopefully in the next couple of days and let you know how it goes

 

I was thumbing through my pics and figured I'd post these.

Be sure those lines on the cam are horizontal as in this pic.



I'm pretty sure this is my kingquad chains. See the new one wasn't much longer.



Here is a quadsport chain, which is much weaker. See how much it stretched.



The quadsports have higher lift cams and weaker chains, so the chains stretch faster. The king is really overbuilt.

 

I used to lap valves too. We all learn the hard way on that

The layer of hardness isn't thick and once it's gone, the valve starts to look like the pic really fast. Even if you buy a new valve, the seat is at the wrong angle so it will wear the valve to match and it's the same story. If I were you, I would take the head to a shop to have a new seat cut. The tool is $250. The valve is about $30 on ebay. Get one made in japan. Either OEM or Vesrah.

I'm kinda curious if you installed the chain tensioner right. If the tensioner was installed wrong, maybe that stretched the chain. But if your chain is that loose, it will not run right at low rpms either. Was the chain loose when you first took it apart?

 

Ok so since i lapped both valves am i going to have to replace both or just one? I also can make my cam line up like that, but when it is sitting slack it looks like its retarded a tooth and if I spin the cam counter clockwise until it tightens up it lines up just like the picture. I'm pretty sure this is the right setting since if i advance it a tooth it runs terrible.

Here is the stock chain


Intake valve that had 4,000 miles on it
The chips in that happened after i had put it back together ran it then replaced the head.

This is the exhaust valve that had the same miles on it. It has zero cupping