SU Help

[3VILC]

Very cliche, but long time reader first time poster
So a quick background, I brought my SJ as a blank canvas, rolling body with nothing in the engine bay. Already intrigued by the SU conversion, it happened that the G16 engine I picked up for it already had an SU on it but had 'carb problems'. While using British carbs might not seem like the done thing on this side of the world, being British born I was determined to get it running
Long story short, the piston was seized in the body and not even a hammer was going to persuade the 2 to seperate so that went in the bin. Picked up a pair of brand new HIF6's brought for a range rover and never used for a price too good to pass up, sold the extra one for almost as much as I paid for the pair, even better Fitted the BDL needle I salvaged from the old carb until I could get a BFM.

So whats the problem your all asking..
Starts fine now, can tune it approximately cold, runs around 2000rpm on full choke, 900ish when first off choke, goes like a cut cat. But after warm up the idle wont drop much below 2000, even with the idle screw wound off the throttle stop, and we eventually get fuel pouring out the overflow.
Best info I could find is the suzuki pumps run 6-9psi, although I see no mention of anyone on here needing to use one I chucked a regulator on and still no change.
If I pull the return line off the pump I get a huge burst of pressure like opening a coke bottle. Blasted the compressor down the line and got a chunk of crud out the other end, stuck the tank end of the hose in a fuel can and engine seemed to run fine and plenty of fuel flow into the can, cleaned out the tank fitting also, reconnected everything and back to the same problem again.
It is possible, as the body had been sitting on a farm for X years with no engine, that the line is full of crap which keep dislodging and blocking the line, so I suppose running new line should be the first bet, and the cheapest since I have a ton of 3/16" copper line left over from brakes. Or prehaps has the pump gone haywire and somehow creating far too much pressure.

What are everyone elses thoughts? Would the float chamber overfilling increase the idle by that much, or do I need more air to be getting in somewhere too? I've dismantled and checked all the guts of the carb, checked float height, needle etc, and the carb had definately never been used anyway, drilled the vac advance on the correct side of the butterfly. Can't find any more vac leaks. Unless the overrun valve in the butterfly is opening on decelleration (i think thats what its supposed to do?) and then not closing again..that would probably cause high idle depending how much air flows thru it.

Anyway, novel over for now
Any thoughts, comments, more things I should check, preferably that don't require spending any more money
Thanks, Clive

[trotter]

presume you've had a read through this?
http://forum.suzukiclubuk.co.uk/vi ... =13&t=2249

I run a mechanical pump with my su so not sure on the pressure's etc... have you tried adjusting the mixture screw as well as the idle? i'm not familiar with the hiff 6 so not sure where to start but if its anything like a hif 44 then there's a fuel air mixture screw. see above link for pics

scottie and twiss will be along shortly with some advice i'm sure

by the way..

where abouts in the world are?

[3VILC]

HIF6 is basically identical to the HIF44, its just measured in the old 1inch + X/8ths sizing (ie 1-6/8th or 1-3/4 = 44.4mm )
Yup have read that thread plenty of times along with any other tuning guides for SUs I can find. Have owned 2 cars with BMC engines and never had a problem tuning either, thats whats bugging me haha.
The basic idea is always the same, set idle, adjust mixture to get highest speed, lean off until speed just starts to drop, richen until max speed is just reached, reset idle, repeat whole proceedure if you want to get more accurate.
Problem is the idle wont go any lower than around 2000 even with the idle screw backed right off.
So im puzzled haha. I am also running the standard mechanical pump, which best research can find is around 6-9psi. So is the pump pushing too much fuel (either because the pump is knackered or the return is still partially blocked) or do I have a second problem like air getting in somewhere as well complicating things. By my thinking, pushing too much fuel and filling the float bowl upto the vent tube would make the engine too rich and die at idle, but I could be wrong hence why I'm looking for other peoples thoughts. Don't know if a stuck open overrun valve would flow enough air to make the idle that high, but its all I can think of, any other vacuum leak would be fairly obvious to increase the idle that much.
So any further thoughts and ideas and things to check would be much appreciated

Clive

[3VILC]

Oh sorry trotter, I'm in New Zealand

Also ordered a BFM needle, yellow spring, and proper damper oil direct from Burlen, which are now fitted and made no difference. As I was informed all the recommended needles BDL, BFM, BBZ are so close together that the engine should run fine on any of them anyway just not at its optimum.
By my reckoning the only thing that buggers out in the pump is the diaphragm, which would certainly cause low pressure and fuel everywhere not more pressure.

[3VILC]

After reading a lot more about these overrun valves (aside from the fact too much fuel is obviously being forced in) the main reason people removed them or soldered them shut was high climbing idle and slow deceleration when the valves spring became weak particularly with the engine warm, which seems to be what I am experiencing, it usually seems to idle ok from startup until you've given the throttle a good stab, probably compounded by the extra fuel thrown in the mix. Given the carbs are new the spring should be ok, but then we are putting the carb on an engine other than which is was designed which my create slightly higher overrun vacuum or something, I have the SJ head on a Swift 16v block so the slightly smaller intake valves could also cause a slight increase in air velocity and also vacuum at idle I guess.
I dont know, Im just throwing theories around that its a cheap and simple fix
Anyone else had this much trouble setting up a single SU from scratch should be easy

[dan_2k_uk]

It has to be more air getting in to add more fuel. The only way for the piston to lift is for the air pressures to change either side of it.

Or the needle seat can drop when the choke is on. Apart from that not a lot else can effect it.

I had some interesting and unpredictable things going on with mine when my choke spindle o-ring was leaking. Maybe if its been sat a long time some o-rings are perished.

[kiwizook]

seeing it works fine off the tank, and has trouble when put back on the tank, I would run new fuel lines, replace the filter, and see what that does. sounds like it is particularly the return line that is playing up, as it hisses at you when you take off the fuel off of it, indicating it is probably trying to pump fuel into it, but it will be blocked, hence compressing the air in the line. this will make your fuel pressure go all haywire. let me know how you get on, I might even simulate a blocked return on my hs2 carb, to see what that does to it.

by the way, where in NZ are you? I'm in Masterton myself, and we seem to have a few more kiwi's on here now

[3VILC]

It seemed ok with the tank disconnected, maybe just didnt run it long enough tho (havnt got fan hooked up yet so cant let it idle for too longer time). When I blow down the line with the compressor with the tank disconnected I can feel the hose expand in my hand so probably partially blocked somewhere still. Will run new lines and hope that fixes that problem. Then just to work out where the extra air is getting in to push the idle up, still suspect that overrun valve so will solder that up and see what happens.. once I get chance to get back out to the shed for an afternoon.
Thought I'd found it the other day, where the adapter bolts to the manifold the bolt under the elbow was shorter (obiously the longest that would fit down the hole with the elbow on top of it) and was only actually engaging about 2 threads and stripped, so pulled it out and ran a bolt up from the bottom with a nut on top so I could get it tight. Changed the gasket again while had it off. Still high idle after a good rev. Has to be the overrun, only place I can think of. Throttle shaft is snug and the rubber seal at the end looks like new rubber so suspect the carbs were well stored and never been used so never had fuel in before.
Oh kiwizook Im in Tauranga. Yep seen a few on here now

[twiss]

Have you tried running it with the fuel filler cap off?
I would have though that if its sucking fuel out and pushing it back into the tank then the pressure should be equal but you never know! If the problem goes away then its probably the tank breather blocked.
6-7psi should be OK I would have thought, probably not enough to break the float bowl seal once its full up... it should fill up, then the pump should chuck the excess back to the tank
might be worth experimenting with an electric fuel pump as they only fill up to pressure, then they don't pump any more... no need for the return line that way

[3VILC]

Thanks for that twiss. Should've mentioned, its not the original tank, Its a fuel cell in the back, well actually one of those portable boat tanks, quite common on offroad only trucks over here. The tank has a vent hose from the cap so no pressure build up in the tank itself. It has to be withing the return line somewhere. Might try running a short line into another container on the ground before I make up a whole new line see if that does cure the problem.
Still not convinced this is causing the high idle tho. Since it seems to be fine until its 'given a stab in the guts' as we would say I'm thinking soldering or otherwise blocking the overrun valve will be the first thing to try and is at least free. Wish I'd read up on the further, would've ordered a plain throttle disc when I got all my bits from Burlen. Then I guess check again for vac leaks.
Will report again once I've had some shed time to do these things. Until then any further suggestions welcomed