Kazuma Meerkat seems to have a Chinese copy Honda 50 engine with CDI ignition.

Magneto baseplate is screwed to magneto cover via 2 small screw-sized circular holes i.e. no rotational adjustment possible.

Hall sensor on magneto baseplate is in fixed position, can't move back and forth relative to flywheel

I can't see it right now because the engine's all bolted up but from looking at a bunch of youtube vids, and from memory, the flywheel is fixed in position relative to the crankshaft with a woodruff key?

I'm figuring from the above, the timing is fixed & I don't need to adjust anything. Am I right?

 

Yes, fixed 99% of newer ATV engines have fixed spark timing. Any alteration in timing is done automatically and electronically by the CDI box.

 

Thanks.

It's become a little hard to start although not impossible, the idle screw adjustment seems very mushy, and it won't rev up without massive bogging even with no load.

If it's not the spark timing it'll be the carb or the valve clearances both of which I've worked on recently.

Valve lash I tried to set to 3 thou each, carb I altered the needle height away from the default middle groove,

I'll try redoing the valve lash maybe a bit wider and put the needle circlip back to the middle groove & retest

 

Best to change 1 thing at a time.

 

ok I currently have..

carb (new off ebay, have had it running ok at one point) removed stripped & cleaned out with compressed air, refitted
slow mixture screw 1 & a 1/2 turns
main needle circlip on middle (3rd of 5) groove
choke & throttle full & free movement
new air filter
both valves allegedly .003" according to my earlier efforts
fuel in tank
new exhaust

It starts and runs but erratically & I can't seem to set anything confidently using slow mix / idle speed screws. It's just "all over the place"

Problems seem to have begun since I decided to buy a feeler gauge & set the valve lash properly. I thought I'd done it to .003" both valves.

Feeler gauge I got was a car / flat bladed type, must admit I did find it very difficult get it in & to feel with it

Changing 1 thing at a time, am going to start with rechecking the valve lash.

[edit]
Rechecked - think I got a better feel for the gauge this time - inlet is somewhere between 4,5 thou; exhaust is a bit tighter at not much more than 3,4 thou

When I first had the machine both valves were wound down tight and it wouldn't start. I got it running fine by loosening the valves off with no feeler gauge and just taking a guess! When I first used the feeler gauge I surmised my guess had resulted in about 8-10 thou. I might try opening them up a bit.

[edit2]
Now got a good stable 4 thou on the inlet valve & a good stable 8 thou on the exhaust. Way above manufacturers specs of 2 thou but I figure it should at least run basically ok with those gaps.

Still giving the original problem. Figuring valve clearances are a red herring. It's almost as if the throttle slide is sticking in the barrel somehow.

When it does run, it sounds lovely. Just can't control it.

Mrs Boulder says I should put the old carburettor back on next. I'm wondering if the throttle cable's the culprit.

 

I'm with Mrs Boulder, clean the old carb out, do not alter any adjusters, if it ran right before dirt/whatever got in, it will run right with the original settings once clean. Check the seals on the inlet manifold are OK when you swap carbs.

 

Old carb cleaned out & back on, seals & gaskets seemed fine.

Still experiencing the problem. It starts easy and goes straight to a very high idle (guess, 1500 rpm?). Throttle response is ok not too boggy. Try to lower the idle using the set screw & about 1500 is as low as it will go, even when the set screw's wound right back off it's seat & the slide is at it's lowest in the barrel. Winding the slow mixture screw in / out makes very little difference except to stall it at the extremes (completely shut or screw almost falling out)

Just can't seem to make it idle steadily anywhere near a nice low idle. If I ever get close, I only ever get a second or two of joy before it goes erratic & then dies in short order

Stripped the now-removed new carb; all the jets & passages seem clear, float height seems ok, choke mechanism works ok..

Pulled the plug just to see, it's pretty black like it's been running too rich

Pulled carb again, cleaned again, jets out & blown with compressed air, visually ok, reassembled carb & inlet with gasket sealant after cleaning & polishing mating faces. Still same.

Tried swapping CDI for another, still same.

I'm pretty mystified at this point. This is the new carb, it's identical to the old one https://www.ebay.co.uk/itm/163413728160

In desperation, opened up valve lash to somewhere around 30-50 thou on both inlet & exhaust. Runs a great deal better. Maybe valves are burnt or something.

 

Sorry to double-post, but got some new info.

To what degree would a fracture in the aluminium intake manifold cause the sort of idle problems I've been experiencing?

I thought I saw something a few days ago but I dismissed it, when on closer inspection I thought it was just a bit of casting flash.

Just now I'd decided to bite the bullet and whip the head off, see what state the valve seats were in.. started by taking off the carb.. loosed off the manifold bolts & pulled away the carb & only half the manifold, leaving the other half of the manifold stuck to the inlet port! Cracked clean in two. I don't know how recently.

I'm thinking now, hold fire with the head removal and valve lapping plan, and just try a new inlet manifold. Sound sensible?

 

Yes, the cracked manifold is probably it. Did notice you couldn't get the idle speed down though. If the new manifold doesn't cure it, check you got the cable seated properly, inner and outer, and that there is some free play in the handlebar lever before it starts to open the throttle.

 

I did remove the cable entirely from the handlebar lever at one point, and looked inside the throat to check the cable wasn't sticking somehow & keeping it open. All seemed fine right down to the slide fully closing off the throat. Nice smooth action, no stickiness. Lubricated the cable and tried running it just using the lead pip on the cable end as the throttle handle. Even with slide fully shut (air filter off) the revs were up at 1500+, with the slow air mixture screw almost completely ineffective at making any change to the running, and the idle speed set screw only able to start raising the revs from 1500+ upwards. Removing the idle set screw completely just left it at the 1500+.

Hopefully not too long before the new inlet comes. Really hoping it cures the prob without having to open up the engine further!