Backfire problem

[graemeno3]

Hi everyone, new member thanks for having me. I've recently purchased 2001 non abs st1100, loving it, however, recently developed a backfire (loud pop, not just your normal popping) on decel, I've read it could be an air leak. I stripped everything back and started to spray carb cleaner in likely places, on the rear left carb intake manifold when sprayed, the revs picked up and it sounded lovely again. My drama is, being very new to carbs, how hard is it to take them out and replace these intake manifolds, also with all the experience on here, is this a likely cause. I'm living in the north east england if anyone knows of anywhere I could take it to get a proper diagnosis.
Thanks everyone again.
Graeme

 

[STAg93]

Greetings, Graeme. It's doable. My '93 had similar symptoms 7-8 years ago. After studying every post I could find on the topic, replacing carb boots, muffler seals, un-PAIR-ing the system, replacing coolant hoses, and doing everything else suggested by the ST gurus "while in there", the bike ran better than ever and still does. That work, an alternator upgrade 15 years ago (28 amp to 40), everything else "while in there", and routine maintenance have carried us over 100k miles and the bike can still outride me.

YMMV though I hope not. It's been worth the work to me.

PS: Carbs have never been rebuilt and valves have never been adjusted.

 

[graemeno3]

Thanks very much for the reply and advice. That sounds a lot, might be a trip to a garage to get work done, I'm dreading that bill haha. But I do want to keep the bike for a long time so will be worth it. Thanks

 

[bdalameda]

It probably need the carbs taken off and new air cut-off diaphragms put it. These are on the side of the carb bodies. There is another thread that describes these.

Honda ST1100 & ST1100A, 1992-2002, Air Cut Off Valve Rebuild Kit - ST 1100 | eBay

Honda ST1100 & ST1100A. New Air Cut Off Valve Rebuild Kit for. Fits 1992, 1993, 1994, 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002 models. Temporarily closes the pilot jet airway to provide a richer mix as the throttle closes.

www.ebay.com

 

[Uncle Phil]

You are fortunate if you can find a shop that will work on a ST1100.
The Honda shops over here will not touch them because they are 'too old' (translated - I can't plug in a computer and have it tell me what's wrong! )
Pulling the carbs is not that big of a deal but I find it easier to do if you remove the petrol tank first (which also is not a big deal - but drain it down first).
Probably a vacuum leak somewhere which would just take some looking.
And I am not sure that UK ST1100s even had the 'pair system' we had over here.

 

[jfheath]

There are 4 tubes that are used to balance the carbs - vacuum tubes. One of these, the rear right, is connected to the fuel cock, which stops the flow of fuel when there is no vacuum.
The other 3 stick up just behind the cylinder heads. They have a small rubber cap that is held in place with a spring clip. The other end is attached to a metal tube down in the depths in the Vee of the engine. A mirror and a torch - (he's up north in England, so is not likely to think I mean a match) - will help you to spot them.

Why am I telling you this? Because if they have become detached - unlikely, or have sprung a leak - possible, then the engine will backfire. If one has become detached, you will know about it. You acceleration drops a bit, down to something like 0 to 30mph in 5 minutes. Each visible movement of the throttle causes the engine to lug and die and pop and bang.

Of course other air leaks will cause similar issues.

If you remove the airbox, there are tubes underneath, which are held in place with spring clips. Make sure that you find the tubes and detach the spring clips properly. If you don't, the tubes spring back and launch the spring clip on a perfect arc to land in the now open inlet port without touching the sides.

That will also make the engine pop and bang .

Me ? No. Not really. Just once.