Isuzu G-series Twin Cam

hey guys,
im having trouble with the timing on my g200.. i've tried just about everything i can think of... from taking the engine apart and realigning the cams (cogs) to setting the front timing chain to an advanced and retarted* setting... on tdc the cams sit half a tooth out of alignment.. originally i thought it was the dizzy i made up which it was. ( running retarded when it needed to run in advance) so i changed the dizzy to one that runs right.... now it runs ok but it blows back out the carbies now and then and out the exhuast....

currently i have it running in 2 degrees advance on the tiing chain.

dohc g200 duel side draught* 44 webbers extracters the usual stuff...

anyone got any clues as to why its not running right?

cheers stuart

this brings back memories from when i tuned my first twin cam exact same problem. in the end we gave it about 28 degrees with about 4 degrees advance when you rev it.what sort of dizzy are you using. the one i had had the vacum advance removed and was nearly locked. you might need to move the dizzy 1 tooth to get this much advance.

i made one up from a pulsar dizzy, ( the top half) because it turns the right way, i cant remember where the cog came from i wrote it down somewhere.... but it sounds like u sorted it out ok?!

we spent days re doing the cam timing over and over. if it runs at all the cams are timed right just keep increasing the timing you might not need as much as i had but it will give you an idea. have the carbies been set up for that motor already. when i finally got my side drafts tuned on the dyno we found out that the previous owner had ago at tuning it himself and had drilled holes in jets and soldered other ones up making it really rich down low and lean up top which was the reason the motor was dead when i got it.

yeah well a few of the ports in the carbie have been soldered up... not sure if it was done proffesionally or not... by turning the timing up wot exactly do u mean? turn the dizzy timing or something else? i also have no idea whether they are the stock cams or not im just assuming they are

99% of the time the cams will be standard due to the fact that you have to modify the buckets to put bigger cams in and its alot of work.
I'd be very carefull if the carbies have been modified like that get it going and get it dyno tuned or atleast tuned by a carby specialist. just put your timing light on the motor and turn the dizzy untill the timing advances. if you get to a point where you cant get the timing to advance anymore because you cant turn the dizzy any further .get the motor at top dead centre mark where the rotor is on the side of the dizzy then pull the dizzy out enough so you can turn the rotor, rotate the rotor the opposite way you have been turning the dizzy untill you can push it back in then start adjusting your timing again. get it too at least 20 degrees with dizzy adjustment both ways preferable in the middle of the adjustment.

ok, thanks for that mate i'll give it a go... ne other tips u might be able to share?

Hmm, I didn't know you have to machine the buckets to fit lumpy cams, what has to be done? Machine part of the bottom off so it clears? Is it expensive?

not so much lumpy cams more so cam's with bigger lift. you need to machine the buckets but you can't take too much otherwise the bucket will comke out of the hole at high rpm. i think you can also modify the head but the people i asked about it didn't want to do it. they said to talk to guys that modify motorcycle heads for some reason i think they are a similiar design and the valve springs buckets and shims might be interchangable. this was a few years ago so i can't remember the exact details.

Ahh ok, makes sense.

As for the motorcycle heads connection - the heads on the twincam were designed and/or made by Yamaha. Isuzu for torque, Yamaha for revs

lower mass of the valve train makes them rev out easier

Eli, Yamaha did toyota heads not Isuzu.

Its rumoured that Lotus did the heads on early Isuzu motors but thats a lot of bullshit. The head is designed by Isuzu and is based on the Escort DOHC design.

Nick-

Ahh okay, you sure? I took my engine to two engine builders (one for head work, one for lower end) and they reckoned it was by Yamaha. Could just be similar though.