Author Topic: Back firing and missing only when cold  (Read 2445 times)

Offline basadia

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Back firing and missing only when cold
« on: November 14, 2015, 07:06:42 PM »
I have an 02 ex police ST1100 which has 158 k's on the clock. Recently it has developed a low speed miss when cold including backfiring (popping) through the carbs. I have replaced the spark plug lead caps with new ones and complete second hand the coils and leads, I have run a full bottle of fuel cleaner through over two tank fulls of fuel on a weekend ride recently.
 
I am at a loss as to what the issue is as it stops when it comes up to operating temperature. Next things I am looking at will be a full carb clean (not looking forward to this one as it seems very daunting balancing the carbs afterwards) and maybe a compression test to check on burnt valves.
 
When I had the plastics off changing the coil today I think the popping was coming from number four cylinder, I might drop the plastics off again and confirm that which carb the popping is coming from. If it is coming from the same cylinder it might be that carb or maybe valve.

Anyone have a suggestion on how to diagnose a fix?

tks

Keith
Keith
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Offline Yorkie

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Re: Back firing and missing only when cold
« Reply #1 on: November 14, 2015, 10:05:32 PM »
If you have to balance the carbs #4 is factory set and therefore not adjustable, all others are balanced to it.
Brian 0418937173
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Re: Back firing and missing only when cold
« Reply #2 on: November 15, 2015, 12:16:04 PM »
Check your intake manifold rubbers for cracks.
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Offline STeveo

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Re: Back firing and missing only when cold
« Reply #3 on: November 15, 2015, 07:17:02 PM »
Check your valve clearances.
 

Offline Brian

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Re: Back firing and missing only when cold
« Reply #4 on: November 15, 2015, 07:31:00 PM »
All good advice /\ ............... One thing to check before you start with all of the above........
First check you have beer chilling in ya fridge :-)
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Offline basadia

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Re: Back firing and missing only when cold
« Reply #5 on: November 16, 2015, 07:37:14 AM »
Thanks for your feedback, I'm leaning towards the valve clearances being tight which makes sense as to why it is popping back through the carby. Sounds like more than a beer week end I'd say maybe a bourbon bottle job. I've not done a valve adjustment so I'm not sure what speciality equipment or tools I'll need to do this job.
I did change my timing belt about 6 months ago and that job left me hesitant to delve back under those plastics again.
Keith
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Re: Back firing and missing only when cold
« Reply #6 on: November 16, 2015, 07:42:50 AM »
Before you jump in, ring up and get a quote from a reliable Honda dealer.   A good dealer should be able to give you a quote over the phone, as they should know how long such a job will take, and just what parts could be needed.
I believe that one of the issues with doing clearances yourself (and I haven't) is that if they are wrong, you need to have a selection of the shims on hand, as you won't know what you need until you've got into the top end and done the measurements.
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Offline basadia

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Re: Back firing and missing only when cold
« Reply #7 on: November 16, 2015, 08:33:22 AM »
I just checked on Epray and I can get a shim kit set from the US for around $120. I'll definitely talk to a shop about a price but I wonder how hard doing the job myself would actually be?
Keith
02 Ex Police ST1100
05 ST1300
 

Offline basadia

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Re: Back firing and missing only when cold
« Reply #8 on: November 16, 2015, 03:28:53 PM »
After making a couple of phone calls I have been quotes around 4-5 hours labour to do the shim plus parts. So at $100/hour I don't see I'm going to get out of this job for less than $500 - $600.
Anyone have a shim kit I can borrow? Happy to replace any shims I use, the kits retail for around $140. That's a lot for a kit that I might use once.
I also might do a compression test before I spend any money on tools, if I have one cylinder that has low compression it is either going to be a burnt valve or tight clearances.
Keith
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Offline STeveo

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Re: Back firing and missing only when cold
« Reply #9 on: November 16, 2015, 06:07:20 PM »
My 94 1100 started doing that on the way home from the Ballarat national rally, and of the left rear cylinder too. Valve clearance was nearly all closed up. I stripped all the plastics off and measured the clearances, took the 'tight' shims to the dealer and he swapped some and I had to buy two. Cheaper than paying them $100 per hour.
 

Offline basadia

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Re: Back firing and missing only when cold
« Reply #10 on: November 16, 2015, 08:01:22 PM »
Must be common for the left rear cylinder as that is the same one that is popping back through the carb. I suspect now that tight valve clearance could be my issue as well. Looks like I'm going to have to pull it apart and sort out the issue, problem is do I buy a kit or pay for single shims as they may end up being close in price. I priced single shims today and the shop wanted $10 per shim, that's $160 to do the whole set if I have to change them all.
Keith
02 Ex Police ST1100
05 ST1300
 

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Re: Back firing and missing only when cold
« Reply #11 on: November 16, 2015, 08:24:48 PM »
Before spending money on shims check your valve clearances. Most could still be within spec so just buy the ones you need.
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Offline basadia

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Re: Back firing and missing only when cold
« Reply #12 on: December 21, 2015, 12:03:36 PM »
OK I ordered a shim kit which took nearly a month the get here from the states had to wait for a decent day to pull all the Tupperware off the old girl. Got down to the camshaft and what do you know all within spec, bugger. Not sure where to go on this now, might have to check the carb tubes as advised above. Lots of work for no fix, not happy.
Keith
02 Ex Police ST1100
05 ST1300
 

Offline basadia

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Re: Back firing and missing only when cold
« Reply #13 on: December 21, 2015, 12:05:38 PM »
Oh and now I have to put it all back together. I also found she had a flat rear yesterday, I've gone nearly 10 years without having a puncture and now I get three in six months.
Keith
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Re: Back firing and missing only when cold
« Reply #14 on: December 21, 2015, 02:00:53 PM »
Back firing either in the exhaust or carbs can also be caused by to much or not enough fuel. If the engine is cold are you using the choke or not? How long has the fuel filter been on the bike as a partially blocked one can cause a restricted fuel flow?
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Offline Abe

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Re: Back firing and missing only when cold
« Reply #15 on: December 21, 2015, 07:37:53 PM »
Sorry, I did not see this post before.

Change a spark plug from a good cylinder and note difference, if any  (eliminates spark plug)

Check spark plug lead, plug and resistance

I'll be doing a carby tune  :thumb, I have a carby snail tuner if this assists you or you can ride to Sydney and I'll do it for you.

You'll notice the difference on the home trip (if it is the carbs though).
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Offline basadia

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Re: Back firing and missing only when cold
« Reply #16 on: December 22, 2015, 08:50:47 AM »
Not using any choke when I start the bike from cold, I've had my ST for 8 years and never needed to use choke but I'll give it a go and see if there is any difference.
I did try and remove the carbs but when I got the cover off I got a bit daunted by the amount of bits that have to go back together and did a visual inspection of the rubbers joiners but due to the limited amount of room I gave up. I did regret pulling the carb cover off as it took me over an hour to get it back on with all the holes lined up correctly on the inlet tubes, what a mongrel of a job that was especially trying to get it over the 4 tubes that come out of the carbs. Not looking forward to doing that job again but as I'm suspecting my back firing maybe carb related it may be inevitable.

spark plugs have only recently been swapped out and I replaced the coils and leads with second hand units a couple of months ago trying to rule out an electrical fault causing the misfire thus the reason I'm leaning towards a tuning problem. If I had a set of vacuum gauges I would try doing a sync but as I'm sinking money into this with no result I'm not willing to drop another $150 with no result.
Keith
02 Ex Police ST1100
05 ST1300
 

Offline Yorkie

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Re: Back firing and missing only when cold
« Reply #17 on: December 23, 2015, 09:53:33 PM »
new spark plugs does not mean that they work, I recently bought 4 for my CB750, one was a dud out of the box.
Brian 0418937173
Manager York Motor Museum

In the shed
1971 CB750K2
1980 XV750
1977 GL1000
FR#720
CMRCWA #133
York,WA

So at what age does this "old enough to know better" kick in?
I believe in the "hereafter", every time I go to the shed I have to think "what am I here after"
 

Offline basadia

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Re: Back firing and missing only when cold
« Reply #18 on: January 04, 2016, 05:41:00 PM »
Thanks for everyone providing me feedback.
I have fixed the issue which was caused by the carbies sucking air around the intake manifold plastic tubes. They had hardened over time and the one for number three cylinder had been badly fitted taking a chunk out of the side of the plastic which caused it to suck air. Thanks heaps to Abe for all his help as it took two trips to his place to diagnose the problem and fit the new tubes. I also replaced the vacuum hose whilst I had the bike striped that far down which ended up being a good thing as they all broke of when we removed them. A carby balance when finished and now the bike is running much better.

Attached are some photos of the damaged manifold tubes.
Keith
02 Ex Police ST1100
05 ST1300
 

Online Shiney

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Re: Back firing and missing only when cold
« Reply #19 on: January 04, 2016, 07:33:44 PM »
Awesome to hear that the bike is running properly again :runyay

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Re: Back firing and missing only when cold
« Reply #20 on: January 04, 2016, 07:45:51 PM »
Great news.
Cheers,
Gary
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Offline Yorkie

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Re: Back firing and missing only when cold
« Reply #21 on: January 04, 2016, 10:00:28 PM »
That is good news, I hope you did the coolant hose while you were in there.
Brian 0418937173
Manager York Motor Museum

In the shed
1971 CB750K2
1980 XV750
1977 GL1000
FR#720
CMRCWA #133
York,WA

So at what age does this "old enough to know better" kick in?
I believe in the "hereafter", every time I go to the shed I have to think "what am I here after"
 

Offline basadia

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Re: Back firing and missing only when cold
« Reply #22 on: January 05, 2016, 09:00:56 AM »
Nah, did a visual inspection and they all looked good. Now that I am aware of what is involved in taking the carbs off I would not be daunted in doing that job again. It is fiddly but doable as long as you have a long Philips screw driver to get to the manifold screws.
Keith
02 Ex Police ST1100
05 ST1300