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Re: Surging

Posted: Sun Apr 11, 2021 12:53 pm
by Mattfinish
Hi Guys,
just wanted to thank Baz for producing his list of probable causes for surging.
In my case it turned out to be perished carb to barrel rubbers and a torn air filter seal. coupled with new chain and sprockets the bike is running great with no bucking or surging.

Re: Surging

Posted: Thu Aug 05, 2021 7:00 am
by Dutch
Hi all, my Kettle isn't too bad for surging but saw this post on Facebook. What's your view on this quick fix without having to remove the carbs from the bike.

I can't believe surging as been a problem since day 1 on Kettles since introducing the CV carbs and Suzuki didn't cotton on to this!!

Not sure if none Facebook users can open this though

https://m.facebook.com/groups/262617174 ... 031022447/

Re: Surging

Posted: Thu Aug 05, 2021 7:13 am
by Alan H
No we can't!! :lol:

Re: Surging

Posted: Thu Aug 05, 2021 6:42 pm
by PaulD738
I always thought Kettles only surged on closed throttle?
If so raising the needle won’t do anything as the needle only comes into play from 1/4 throttle up.

Re: Surging

Posted: Thu Aug 05, 2021 8:41 pm
by wardy
I found the same result after fitting the jets from Baz.my bike runs very well now.. I also raised the needles one notch as I'd seen that helps with surging also. To be honest, i could not tell any difference, so they are going back to std ( in the middle)
I also found that fitting my accent ignition last year made a big difference to idling and my bike has never ran so well in the 17 years I've owned it.

Re: Surging

Posted: Thu Aug 05, 2021 10:05 pm
by teazer
More Facebook misleading "information".

That said, all large capacity two strokes have a tendency to surge on low throttle opening. On say an RD400 that was fixed by drilling a hole above the exhaust port to bleed off compression pressure at low revs which was a factory feature and more or less worked. Surging on a GT750 isn't limited to CV carbs and sometimes is an issue on J/K models as well.

A needle change makes most of the range a little richer and it is possible that's all that some bikes need, but as has been pointed out, it can't fix the closed throttle situation. With closed throttle especially on the over run (slowing down) the situation is closed throttle and high vacuum that is too lean because it "sucks" too much air in through the pilot air jet under those conditions. The fix to that situation is smaller primary air jets not bigger pilot jets or higher needles.

But if you have a surge at cruising, then raising the needles might alleviate that somewhat. Our bikes pre-date the move to super lean jetting to get through emissions tests, but I wouldn't be surprised if Suzuki jetted the GT750 slightly lean at cruising to somewhat improve fuel consumption.

I thought I had seen a post by Baz some time ago that said that the fix might be different for different bikes and each needs to be corrected appropriately.

Re: Surging

Posted: Thu Aug 05, 2021 11:42 pm
by Alan H
teazer wrote: Thu Aug 05, 2021 10:05 pm That said, all large capacity two strokes have a tendency to surge on low throttle opening. Surging on a GT750 isn't limited to CV carbs and sometimes is an issue on J/K models as well.

Not if the carbs are set properly. GT550s don't surge and they don't have cv carbs. Dunno about other models as I haven't ridden them, but the 750 is the only 2 stroke with cv carbs.

Low tickover and non cv carbs is the answer. People tend to forget that we used to ride 2 stroke more aggressively ,'back then' and now most of us think ££££ when YOU ride them. 2 strokes like to be revved, bolox to fuel economy at less than 4k rpm. If you drive like that, get a 60s BSA..

Re: Surging

Posted: Fri Aug 06, 2021 8:58 am
by Dutch
Thanks for your comments guys, for those that use Facebook and have access to it :lol:
I know there is a lot of incorrect info on FB but thought I'd pass it on to you just for your opinion.

As I mentioned earlier mine surges slightly when easing of the throttle but more so when in 5th gear, if this helps!!
The problem I have is reducing my idle speed to 1000 rpm without the engine cutting out. I can of course open the throttle slightly when stationary but is not ideal and really need to fit the mod to get more voltage to the coils so I can then hopefully reduce the idle speed.
At the moment it's idling at approx 1300 rpm and all is ok apart from the slight surging and it runs very well with good mpg but I'm a bugger and thrive for perfection!!

I saw a wiring diagram on here a while back as to how to do the mod to get more voltage to the coils but can't find it so if any of you guys can put it on again I intend to make this my job to do over the winter months.

Thanks again
Regards Jeff

Re: Surging

Posted: Fri Aug 06, 2021 3:58 pm
by teazer
In a stock set up, power comes from the battery along the red lead to the keyed switch and from there an orange wire goes to the RUN-KILL switch and from there to the coils, dropping volts along the way. The cure is to cut into that lead to the coils (it also feed other circuits, so take care to cut off only the three leads to the coil 6 pin connector.

Use the old orange lead to switch a relay. Take power from the fuse box if you fitted one, and from a fused wire straight from the battery on a stock loom to the relay. The other side of the switched relay should connect to that 6 pin connector and the last terminal on the relay goes to ground (earth). After those changes, power through the switches will only be used to trigger the relay and will carry much less power. And the coils will now get full battery power.

https://tops-stars.com/wiring/ignition- ... g-diagram/

You can use standard 4 pin or 5 pin relays but I refer to use panasonic micro relays which are sealed and smaller. http://www.easternbeaver.com/Main/Elec_ ... elays.html That's where I usually get mine, but if you have a local source, go for it.

Re: Surging

Posted: Fri Aug 06, 2021 4:05 pm
by teazer
Alan H wrote: Thu Aug 05, 2021 11:42 pm
teazer wrote: Thu Aug 05, 2021 10:05 pm That said, all large capacity two strokes have a tendency to surge on low throttle opening. Surging on a GT750 isn't limited to CV carbs and sometimes is an issue on J/K models as well.

Not if the carbs are set properly. GT550s don't surge and they don't have cv carbs. Dunno about other models as I haven't ridden them, but the 750 is the only 2 stroke with cv carbs.

Low tickover and non cv carbs is the answer. People tend to forget that we used to ride 2 stroke more aggressively ,'back then' and now most of us think ££££ when YOU ride them. 2 strokes like to be revved, bolox to fuel economy at less than 4k rpm. If you drive like that, get a 60s BSA..
Exactly. Carbs have to be set up correctly and BS40 were not set up perfectly stock. And you are also right (don't tell anyone I said that please. It's our secret.) We tend to ride a lot slower and less aggressively because the bikes are older and so are we and traffic is way more heavy than it used to be. If I want to travel slowly and smoothly, I'll take the car. When I ride a bike, one of the things I enjoy is the sensation or feeling of acceleration and braking. I don't have to pretend to be Barry Sheene (showing my age again?) but it's nice to use some of that power from time to time.

Yes it's nice to ride slowly and smoothy, but that's not what bikes are about. :?