Electrical geniuses please speak now!

Rob are you suggesting that I might still have carb blockages? As I understand it I am probably getting the stumbles with 1/4 to 1/3 throttle, which should be in a position controlled by the needle and emulsion tube. This is definitely clear, it has a big bore and all the smaller drillings through the side are also open. The main jet which resticts the flow is also definitely clear. The air supply from the plenum chamber is also open. The diaphragms are 100% fine and sealed, and the slide hole is clear so venturi vacuum is reaching the vacuum side of the diaphragm.

What is apparent is the problem has persisted throughout all my carb meddling; I have disassembled, cleaned and reassembled 3 times, going further into the air side of the carbs each time, yet the stumbling hasn't changed it's onset or severity, which makes me think it is caused by something external to the carbs. Old fuel is one such factor, as is fuel delivery to the carbs, or the ignition system. I have fully tested the fuel supply so I know that to be OK, and the resistance checks for ignition coils were very close to or within spec.

 

Squirrelman is probably the guy you need to talk to.

 

You STOLE that bike!

Yeah, I've used a Honda Civic fuel pump on an '82 Magna ... it works.

I'd like to see the plugs if / when you get a chance and drain the old fuel and fill with fresh before you do anything.

Is that unit equipped with an auto fuel shut off valve? I know some of the early 2000's were. It's vacuum operated and could cause starvation in the higher RPMs. If the fuel system was that gummed up - then that could be gummed up too.

 

Thanks Jeff

I have taken the vacuum petcock out of the system before I started into the carbs, I had read that it can give grief. Given the need for a fuel pump I did not see any need for a shut off valve too.


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What have you done in regards to the rubber manifold carb boots (insulators in Honda speak )
They weren't too expensive for a new set of 4 and remember not to over tighten them as this can cause vacuum leaks

Honda on the Vfr Vtec specify I think from memory around a 7 mm gap between the inner ends of the clamp

My 2004 actually split 2 when i replaced the thermostat and it was nearly impossible to see only showed up when spraying WD40 around the boots whilst the bike was running

Yeah ditch that fuel use it as weed killer don't even try it in the mower

I drove road tankers for BP in NZ and have seen how quick
Modern fuels can turn to to a useless fluid quicker than most would think ,petrol without stabilizing additives will be going bad in less than 3 weeks

Even high octane aviation gas used to be mixed with premium 98 RON fuel to make race fuel if it didn't get turned over quick enough

 

Jeff plug photos attached, cylinders 1 - 4 l - r.

James the boots all look good, I inspected them closely. Also the carbs balanced v easily which I don't think would happen if the boots leaked.

Thanks for your help guys.


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Here's a guide to help you diagnose the plugs:

http://www.ngk.com.au/spark-plugs/technical-information/spark-plug-analysis
http://www.autolite.com/media/11838/plugtips.pdf

It's hard to tell by the colour of a photo ... 1 - 2 look to be OK provided that the white colour isn't a fuzzy loose powder (this indicates ash which means that oil is getting into those cylinders). They appear to be healthy.

3 - 4 look darker / possibly sooty (hard to tell as they appear to be newer plugs). These are the cylinders that might be misfiring. You will want to inspect these a little closer. Do the plug tips smell like fuel on these?

Are 1 - 2 on the same bank and 3 - 4 together on the other bank? Your plugs should all be about the same colour since the V4 on a ST1100 is mounted out the sides vs. along the length of the bike (equal heat).

 

Plugs 1 and 3 are the left front and left rear, plugs 2 and 4 are the right front and right rear. All were new, with maybe 150km of use.



This is the same photo but without flash. The ground electrodes of 1 and 2 are bright, clean metal. 3 and 4 do look more sooty. I assume that a misfire usually leads to unburnt fuel and soot?

I've cleaned the plugs and re-installed them, and also pumped the tank empty. I'll get some fresh fuel today and give the bike another run this evening. Its most annoying when paid employment gets in the ways of motorcycle diagnosis!

 

Damn jobs. LOL

That photo with the flash is a lot better to see compared with the first.

Yes, I think you're on track with that diagnosis. This could be a result of shitty fuel mixed with the new stuff not burning properly. The rear plugs don't look too bad but the electrodes themselves and their insulator look very sooty. These are new plugs, yes?

I'll wait until you can get some fresh fuel through there and run the bike a bit. Give it a while for the fresh fuel to make its way through.

 

Thanks Jeff; I'll have a beer in your honour this evening, and let you know how I get on.

 

I think that only applies to the VF/VFR. The ST mounts the V4 cylinders so they run side to side (vs front to back on the VF/VFR).

The rear cylinders on a VF/VFR are jetted differently than the front because of the position of the cylinders in the frame (cooling and intake) if memory serves correctly.

 

Thanks guys. I have kept individual carb parts separate so I know I haven't switched any parts. Doesn't mean someone else may not have done so earlier though so I'll check the part numbers and see if there are differences.


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Well firstly there are no differences in jets/emulsion tubes or needles in the carbs. Tink I'm sure you'd find your way around the carbs no problem, the engine is just like any other V4, carbs are a bit of a pain to wrestle on and off, but otherwise the bike is easy to work on. I don't own an air compressor so was a little limited in my ability to blow hard through the air passages, but I did my creative best with a tyre pump and football filling nozzle and definitely was blowing clear through all passages after liberal use of carb cleaner. It's good to hear that I may only need to tear them down one more time to get this right!

Tonight I drained as much of the old fuel as possible and then refilled the tank to the brim at a service station, I would guess there would be no more than 1L of old and 27L of new gas now. Sadly, no real difference to the running problems.

The plugs aren't showing any significant visual differences, I have tan deposits on the porcelain of all, maybe #1 is a little darker, but I only rode for 20km so might be a little premature.



I would say the bike is possibly running a little better each time I head out, I had it up to redline tonight and the hesitation might be a little less. I wondered what effect 8 years parked might have had on the rings and valve seats and whether it is taking a bit of time to get everything to bed in again.

I have been riding the bike "dirty" (borrowed this term from another post I read); unregistered, unwarranted, and with an expired licence plate. The good news is if I get my collar felt, it is only a $200 dollar fine (when a year's registration is $580), bad news is 20 demerit points on my licence...My wife has been understandably disapproving, so I will do the decent thing and hopefully get legal tomorrow.

 

The plugs look healthy ... except the one cylinder .. the plug looks darker and wet? Can you verify? The photo is a bit fuzzy. What cylinder is this? If it is wet'ish - check for good spark and the condition of the wire. If it's not wet'ish then it's probably fine (hard to tell from the current photo).

I was actually going to ask in my last message if you've done a compression / leak down test on the cylinders, that sitting for so long, one/several of the rings and/or valves could be sticking a bit. If you think this may be the case, remove all the plugs, put some 'SeaFoam' in each cylinder and let it sit ... DO NOT put the plugs back in. Suction out the fluid afterwards (try to get it all), turn the engine over with the kill switch on for a short while to try and remove anything left in there, put the plugs back in, and fire it up ... this will help remove excessive carbon deposits. You will also want to do an oil change within 500km's in case some of the SeaFoam makes its way down into your oil (which is fine - it will help clean the engine but don't leave it in too long or it will thin your oil).

I know the Toyota Highlander I rescued last year had been sitting for some time and as a result, it stumbled on the high end, especially under heavy load until I put a few tanks of premium through it.

 

My guess - and it is just that - is that given the cylinder vacuums are even according to my sychroniser, the valves and rings are probably seating/sealing fine, at least at idle.

 

Possible ... it's hard to tell at idle sometimes, but it was just a stray thought more than anything.

Wish I was closer, I'd love to get my hands on that bike and take a look for myself. Diagnosing over the internet can be difficult sometimes. You run it some more with the new fuel since? Get any stronger? You mentioned it 'seemed' to be getting a little better.

 

No just the single run last night around my local suburb. I made a point of keeping the revs up around 4k (the 1100 is very happy at car-like rpm, 1500-2000 is plenty for city streets) and I imagined it was feeling happier with this, but the engine wasn't under much load. I need to get our on the open road and I'm working towards getting fully legal for that tomorrow.

I was thinking the next way to share my problem would be an on-board video so you can hear what I hear.

I appreciate your interest and assistance, keep it up.

 

I love fixing stuff ... especially engines and other mechanical wonders ... it's as much as an adventure as actually riding is sometimes.

 

Me too. I enjoy participating in the online forums and trying to diagnose other's motorcycle-related problems, as it forces me to think laterally about cause and effect. I will sort out my ST! Mind you, after the "fun" of removing and reinstating carbs, blowing through jets and setting floats, I'm starting to pine for the simpler days of EFI!