GS550 spluttering at low revs after new coils

[Guest]

Hi Guys
I finally decided to join the forum after getting loads of information off of here, thanks to all the experts out there who contribute.

Let me start from the beginning. So I bought a GS550L 1981 and straight away started converting it to a cafe racer (didn't ride it much at all). I've now finished the project but just fixing a few issues. The original problem was that after a good long ride on the highway the engine would get hot and when I would come off the highway and sit in traffic it would rough idle and if I didn't keep the revs up it would stall and not start again for at least 15 min after it had cooled. The other issue was that occasionally if it is cold outside it won't start and I'll have to jump it off my car battery. The other day it wouldn't start off of my car battery even though it was spinning over very fast. It eventually took me 15 min to get it started. I had look at a few options , changed oil, oil filter, fuel filter, cleaned the carbs, new spark plugs and now finally have replaced the coils. Dont get me wrong once she is running she runs fine, if I don't go mad and ride around town she doesn't get hot or stall. (I'm now suspecting that it may be the exhaust wrap that could be the problem with the over heating and stalling, not sure yet)

So anyway I put on some AI pattern high performance ignition coils on which I bought new off eBay from a local UK supplier , they were both exactly the same so I wired them up exactly the same as the original two were wired. Started her up, started instantly, idled nicely, reved up nicely but as soon as I pop it into 1st gear and pull off it's spluttering until I get it into 3rd gear and the revs are up and then it goes fine. Well feels fine anyway.

Point to note I never had any spluttering with the old coils.
I have the correct spark plugs but do I need to upgrade the spark plug specifications? Are the new coils more highly powered? It's almost as if the coils aren't performing properly until the revs are increased. I've checked the HT leads and the spark plugs sockets are screwed in properly. The leads are also correctly laid out ie 1, 4 2,3
Any thoughts on any of my issues namely:
Stalling and rough idle when hot (thinking it may be the exhaust wrap)
Occasionally not starting even when hooked up to my strong car battery(eventually starts on car battery and rules out needing a new battery)
Spluttering at low revs with the new high performance coils

Thanks in advance guys.

[tom203]

Welcome.
Since you've been lurking ,you must have noticed the importance of proper carb cleaning, so just how did you clean yours?
The stock suzuki ignitor is likely fussy about the ignition coils - stock coils measure about 4 ohm primary- what do these new coils measure?

note all the stuff about charging issues on these old critters..... have you checked yours?

[Lomomoon]

Welcome.
Since you've been lurking ,you must have noticed the importance of proper carb cleaning, so just how did you clean yours?
The stock suzuki ignitor is likely fussy about the ignition coils - stock coils measure about 4 ohm primary- what do these new coils measure?

note all the stuff about charging issues on these old critters..... have you checked yours?

Hi Tom

Thanks for the reply. I had the carbs sonically cleaned. Not sure what the new coils measure. I've been trying to find some specifications for them online but no luck. I'll try get a tester to see what they are pushing out.
Any suggestions or links on a new ignitor?

[hampshirehog]

Are you running with the original airbox fitted plus is the vacuum hose attached or nipple blocked off?

[Lomomoon]

Are you running with the original airbox fitted plus is the vacuum hose attached or nipple blocked off?

Hi , yeah original airbox and the vacuum hose is attached (I'm assuming you are talking about the vacuum hose from the carbs to the tank?) In the way of the engine , everything is still stock including the exhausts, nothing has changed except the coils.

[hampshirehog]

When you had the carbs ultrasonically cleaned were they completely split down or did whoever cleaned them dunk them in only partially stripped? I've sorted out loads of 'cleaned' carbs by cleaning them. My guess for the poor starting is that the choke wasn't / isn't working properly - the pick up hole in the bowls is often overlooked. She should start on the button and immediately rev pretty high on the choke circuit. Plus did you replace the o rings? 30+ years old rubber could be another problem.

This is of course based on the old adage that most ignition problems can be sorted by dealing with the carbs!

[Lomomoon]

When you had the carbs ultrasonically cleaned were they completely split down or did whoever cleaned them dunk them in only partially stripped? I've sorted out loads of 'cleaned' carbs by cleaning them. My guess for the poor starting is that the choke wasn't / isn't working properly - the pick up hole in the bowls is often overlooked. She should start on the button and immediately rev pretty high on the choke circuit. Plus did you replace the o rings? 30+ years old rubber could be another problem.

This is of course based on the old adage that most ignition problems can be sorted by dealing with the carbs!

I would imagine that they were done 100%, the guys I take my bike to are renowned in the city for doing good work. The choke does work as I use it to start the bike, when used the bike revs up high. Since installing the new coils it seems to start right on the button now but can't be 100% as the starting issues comes and goes.

At the moment the biggest problem I'm having is the sputtering at low revs after installing the new coils. If I can get the bike running properly with the new coils then I can take it out and give a good long ride and see if the other two problems persist.

[hampshirehog]

The intermittent starting issue - does it start poorly after you've left it for a few days? If so the solution to that could be switching your petrol tap to prime for 30 seconds or so before you hit the starter button (and turning it to on after it's started).

Another thought, did you put new rubber plugs in the carbs, the ones that cover the pilot jet so that the fuel is first metered by the main? If so were they genuine Suzuki? The commonly available pattern ones are a lot cheaper (genuine are a rip off at £4 a pop) but they melt in modern fuel and gum everything up.

Have you got a link to the coils on eBay? So that we know which ones you've fitted.

[Lomomoon]

The intermittent starting issue - does it start poorly after you've left it for a few days? If so the solution to that could be switching your petrol tap to prime for 30 seconds or so before you hit the starter button (and turning it to on after it's started).

Another thought, did you put new rubber plugs in the carbs, the ones that cover the pilot jet so that the fuel is first metered by the main? If so were they genuine Suzuki? The commonly available pattern ones are a lot cheaper (genuine are a rip off at £4 a pop) but they melt in modern fuel and gum everything up.

Have you got a link to the coils on eBay? So that we know which ones you've fitted.

I'm glad you mentioned that, regarding selecting prime, I thought of that yesterday after taking my tank off to fit the new coils. I will try this again when she is running and yes she starts poorly after standing for a while(normally) the recent poor start (took 15min off of my car battery)was only the morning after riding her in the afternoon ,but it was ealry morning and we had had a storm the night before (was before the new coils).

Regarding the carbs, I never did them myself, they were professionally done by my local mechanic, basically they are the best in the city, so I've been told by various unrelated people in the bike industry. So unfortunately I cant answer that question. But for now I want to rule out dirty/blocked carbs.

Here is the link...

http://www.ebay.co.uk/itm/401300883190

[hampshirehog]

Those no- name coils are fine and just plug and play for many Japanese bikes from the day. They won't be causing a problem (unless they're faulty, which is very unlikely).

I'm still minded that your issues are fuel related. Try leaving the tap on prime all the time (until you turn the engine off). Could be a faulty diaphragm. Failing that I'd pull the carbs off - they're simple to work on and there's a really clear guide on here about how to sort them. Maybe ring your mechanic and ask if he cleaned them as per the guide - there is no other way though many have tried to find it.

[hampshirehog]

One other thought. Have the valve clearances been checked?

[Lomomoon]

Those no- name coils are fine and just plug and play for many Japanese bikes from the day. They won't be causing a problem (unless they're faulty, which is very unlikely).

I'm still minded that your issues are fuel related. Try leaving the tap on prime all the time (until you turn the engine off). Could be a faulty diaphragm. Failing that I'd pull the carbs off - they're simple to work on and there's a really clear guide on here about how to sort them. Maybe ring your mechanic and ask if he cleaned them as per the guide - there is no other way though many have tried to find it.

Ok thanks
The sun is out so I'm going to whip the tank off again. Make 100% sure that the power leading into the coils is connected properly (already checked the HT leads) and then take her out. You mention above about leaving the tap on "prime", is this to try and cure the stuttering after new coil installation? If that doesn't work I'm going to pop the old coils back on and go for a spin because I know for sure there was absoultely no stuttering with the old coils on(just want to see if the problem persists it goes away) Failing all that I will take the carbs off.
Quick question I just thought of, while the bike is running , if I take off spark plug 2 or 3 the bike still runs (obviously minus a cylinder) if I take off 1 or 4 the bike dies straight away. Is that normal? Just thought I would add that incase it rings any bells.
Also I shouldn't need to upgrade my spark plugs or anything like that after the new coil? 4 weeks ago I put new NGK plugs in according to the specs.

[hampshirehog]

Leaving the tap on prime eliminates a faulty vacuum system - nothing else. I presume your tap is 30+ years old and they do play up at some point.

I was unclear that your stuttering problems only started when you changed the coils so sounds like a plan to swap the old ones back on. Ref unplugging 2 & 3 and it running but not 1&4 that's not normal. obviously those pairs run from the same coil so that would indicate a coil problem, though not prove it. Could be valves (2&3 run a little hotter as they're in the middle so that might show earlier) or could be a problem with the carbs - they're a tad trickier to set up in the middle. Could also be a duff carb balance.

Could also be dodgy plugs. Over the past 5 years or so either NGK have let standards slip or more counterfeits have found their way in to bikes or something else. Worth trying your old plugs to see if that helps. You won't need to upgrade plugs with a change of coils.

Just started raining here and I'm only 30 miles north of you. Hope you stay dry on your test run!

[Lomomoon]

Leaving the tap on prime eliminates a faulty vacuum system - nothing else. I presume your tap is 30+ years old and they do play up at some point.

I was unclear that your stuttering problems only started when you changed the coils so sounds like a plan to swap the old ones back on. Ref unplugging 2 & 3 and it running but not 1&4 that's not normal. obviously those pairs run from the same coil so that would indicate a coil problem, though not prove it. Could be valves (2&3 run a little hotter as they're in the middle so that might show earlier) or could be a problem with the carbs - they're a tad trickier to set up in the middle. Could also be a duff carb balance.

Could also be dodgy plugs. Over the past 5 years or so either NGK have let standards slip or more counterfeits have found their way in to bikes or something else. Worth trying your old plugs to see if that helps. You won't need to upgrade plugs with a change of coils.

Just started raining here and I'm only 30 miles north of you. Hope you stay dry on your test run!

I've just spent past 2 hours working on her in the rain (have just bought a new house with a garage, whoop whoop)

-Took her out with the tap set to PRIME - no change
-Swapped out the new coil that feeds 1+4 and stuck the old coil back on - no change(took out 1+4 because this was the one that made the bike cut out if I took cap 1 or 4 off)
-Fitted both old coils back on - Bike goes like a dream!

In conclusion: My bike DOES NOT like the new coils.

Problem 1 - Spluttering with new coils fitted - Solved - Solution: don't use new coils
Problem 2 - Struggling to start after standing - Inconclusive for now - Solution: Will try setting the tank to "prime" before starting after long periods
Problem 3 - Rough idle and cutting out after long periods on the motorway or engine is very hot - Not solved

Regarding problem 3, I thought I might treat her to some new coils, after all they are 36 years old and hopefully improve my performance, while at the same time see if it solves the rough idle and stalling issue. Iv'e been told by a mechanic that when they get really hot they cook the fuel in the carb bowls and the fuel evaporates therefore rough idle and a stall. Doesn't really explain why it wont start again for 10-15 min, and also if this is a common problem then surely it would do the same if the bike was brand new. I must add that I have wrapped my exhausts a while back so this may be the cause but as far as i was aware the wrap is meant to force the heat through and out the exhaust, preventing it from escaping into the air around the engine, so if anything it should help. But I may be talking rubbish. I never really rode the bike after buying it and wrapping the exhausts so cant say if this is the cause.

Other than that the bike rides perfect until it gets really hot. But around town she wont cut out. Anyone have any thoughts?

[hampshirehog]

Wrapping your exhaust won't have affected anything - your bike in standard fettle isn't fussy enough to notice that.

If she's running fine when she's not very hot then it's not ignition nor fuel. Which suggests valve clearances (it won't be fuel evaporating out of the carbs - they're insulated from the heat, you can touch the float bowls at any time to see that they're cool). If you've got a compression tester plug it in when the bike is hot and at WOT. I forget what the specs are but roughly anything less than 100 psi and you need to investigate; it'll probably be valves. The specs are on here somewhere. In any event, if the clearances haven't been checked recently you should do them - probably one of the biggest problems leading to a GS going to the graveyard (OK, also dodgy charging systems ). Poor cold starting is often down to no valve clearance as well.