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ST170 on bike carbs, barely runs.
Nickp - 26/10/18 at 08:14 AM

Got the ST170 into my Quantum and have fitted ZX6 bike carbs. Ignition is ST170 crank sensor (Zetec 1.8 flywheel) into Ford ESC module triggering a Zetec coil pack.
First turn of key and it fired up and idled. So I finished off cooling system and made a throttle linkage etc.
It fired straight up again but won't take any revs at all, just bogs or spits back through carbs. Plugs are black sooty which points to a rich mixture, or a mixture that's not been fired correctly. It settles down with a rhythmic misfire which can also be seen with the timing light, which would point to an issue with the ign system. I made up a TDC marker for the lower pulley as the ST170 has none and it appears to be ticking over at 10deg btdc as it should but has a constant misfire when viewed.
The carbs are fed by the bike pump and I've spoke to Bogg Bros and it seems I've done everything right with the setup and it should just run according to them. I tried dropping the float level and even switched off the pump, but at no point did it begin to run better right up to running out of fuel.
Also checked the cam timing, done a compression and leakdown test and all seems OK mechanically.
So, I'm back to the ign system. I'm going to get an ESC module and coil pack to try as they're handy to have as spares, but any other ideas?

Mash - 26/10/18 at 09:51 AM

I'm a complete novice with all this modern stuff so this my be complete bull, but could it be something to do with the VVT?

I'm pretty sure that WASA will be able to answer if not.

Nickp - 26/10/18 at 10:35 AM

quote:
Originally posted by Mash
I'm a complete novice with all this modern stuff so this my be complete bull, but could it be something to do with the VVT?

I'm pretty sure that WASA will be able to answer if not.


No probs at all, thanks for the input and I did start to wonder the same. That's why I activated the vvtpro solenoid with 12v yesterday, but it just made it worse with constant spitting back through all 4 carbs. I've got a VVT PRO to fit but need to get the basics right first.

theduck - 26/10/18 at 11:06 AM

Isnt the ESC module locked to 10* timing when ran by itself?

davidimurray - 26/10/18 at 12:39 PM

Have you balanced the carbs? I found that mine were very sensitive to being correctly balanced and if not you get a mis fire as one cylinder is leaner than the others. Get them balanced well and you can balance a 20p piece on end on top of the cam cover

Have you cleaned and serviced the carbs? Pilots are a nuisance on these and the block if you leave the car standing - I strip and clean them every winter if not used. So more info on this thread http://www.locostbuilders.co.uk/viewthread.php?tid=201193

Nickp - 26/10/18 at 01:00 PM

quote:
Originally posted by theduck
Isnt the ESC module locked to 10* timing when ran by itself?


No, that's EDIS. ESC should give a fixed (not programmable) ign curve starting from 10deg and increasing with revs. Won't be ideal but should be near enough for now.

jossey - 26/10/18 at 01:10 PM

Is the bike pump gravity fed? They don't like to pull upwards.

Nickp - 26/10/18 at 01:12 PM

quote:
Originally posted by davidimurray
Have you balanced the carbs? I found that mine were very sensitive to being correctly balanced and if not you get a mis fire as one cylinder is leaner than the others. Get them balanced well and you can balance a 20p piece on end on top of the cam cover

Have you cleaned and serviced the carbs? Pilots are a nuisance on these and the block if you leave the car standing - I strip and clean them every winter if not used. So more info on this thread http://www.locostbuilders.co.uk/viewthread.php?tid=201193


The carbs were really clean tbh, I balanced the throttle plates and have set the idle screws equally in various positions from 1-3 turns out.
This seems much more serious than just a bit of carb imbalance or jet blockage, I literally can't rev it at all.

Nickp - 26/10/18 at 01:15 PM

quote:
Originally posted by jossey
Is the bike pump gravity fed? They don't like to pull upwards.


It won't even run with no pressure to the carbs, just what is in the bowls.
BTW pump seems to pull from the tank OK, first thing I checked when fitting it.

r1_pete - 26/10/18 at 01:17 PM

Are they the Mikuni carbs with plastic caps held on with 4 screws?

If so check all those plastic tops and the diaphragms are properly seated and sealed. Several years ago I had the same symptoms on a zetec, and it was down to leaks around the diaphragms. A smear of rubber lube in the diaphragm seating helps.

Nickp - 26/10/18 at 01:38 PM

quote:
Originally posted by r1_pete
Are they the Mikuni carbs with plastic caps held on with 4 screws?

If so check all those plastic tops and the diaphragms are properly seated and sealed. Several years ago I had the same symptoms on a zetec, and it was down to leaks around the diaphragms. A smear of rubber lube in the diaphragm seating helps.


No, but similar, just 2 screws in the plastic caps on these. I'll give them a smear either way ta.

davidimurray - 26/10/18 at 04:32 PM

quote:
Originally posted by Nickp
quote:
Originally posted by davidimurray
Have you balanced the carbs? I found that mine were very sensitive to being correctly balanced and if not you get a mis fire as one cylinder is leaner than the others. Get them balanced well and you can balance a 20p piece on end on top of the cam cover

Have you cleaned and serviced the carbs? Pilots are a nuisance on these and the block if you leave the car standing - I strip and clean them every winter if not used. So more info on this thread http://www.locostbuilders.co.uk/viewthread.php?tid=201193


The carbs were really clean tbh, I balanced the throttle plates and have set the idle screws equally in various positions from 1-3 turns out.
This seems much more serious than just a bit of carb imbalance or jet blockage, I literally can't rev it at all.



There is clean and there is clean. I had an issue for months when I first built my car with these carbs. Could never get rid of a misfire, I tried cleaning the carbs by blowing through with carb cleaner. In the end I took all the jets out and soaked them overnight in a mug of carb cleaner. Loads of black scum came out of the pilots, before that I did that every time I touched the throttle it started popping and banging like a machine gun.

How have you balanced the throttles - using a manometer?

big_wasa - 26/10/18 at 04:36 PM

The esc will respond to load and temperature.

Have you connected the vacuume ? Not easy with bike carbs but shouldn’t stop it running.

Early esc’s had one temperature sensor and later ones had two, air and coolant. From memory if either of these are open circuit it gives a default value of minus 40 degC. These will affect things.

Nickp - 31/10/18 at 05:10 PM

Finally sussed it!! And yes it was something daft (which is often the case).
Got back from a long weekend in Barcelona last night hoping my ignition 'spares' would've arrived from ebay, but they hadn't. So I went in the garage today and took on board some of the comments off here. I cleaned the carb jets etc and greased the diaphragms too. Put it all back together but it was still the same.
Earlier I'd googled the crank sensor polarity but wasn't able to find much info when using the ESC module so I cut the wires and swapped them over anyway. Bingo!! Runs like clockwork and revs up lovely, really responsive
So I was kinda right suspecting it was ignition related but didn't expect the loom that came with the ESC module (bought off ebay) to be wired arse about face. It would've been much easier to fault find if it was just a non starter
Ahhhh well at least I can crack on and get it finished now