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Joined: Feb 22, 2011 Posts: 20 Location: UK ´Stockport´
Posted: Mon Mar 28, 2011 2:32 pm Post subject: 1976 GT500a Carb problem
Newbie to the site so Hi to everyone and just hoping I'e posted this correctly.
I have recently finished rebuilding the carbs on my 1976 Suzuki GT500a, the bike started up no problem, ticking over around 1200 rpm, I decided to give it a run round the estate and she pulled well througout the gear changes even at lower the revs, however after parking up for a short while I was unable to fire the bike up again, sparkplugs found to be saturated proberly due to kicking over a few times and flooding, after drying the plugs out the engine started but would only run if I held throttle above 2000 rpm also the engine was surging a little but if I ease off the throttle the engine cuts out, this time I removed plugs without trying to kick over again and found them to be saturated so I presume it must be running to rich, all parts replaced on the carbs are from suzuki with there corresponding numbers as per specs/sizes but with only 2 exception the first is the Mikuni Jet Needle 5FP17-3' which is now obsolete so I replaced this with the 5FP17-5, does anyone know if these are different and maybe I would have alter the setting position for a leaner mix, the second I have replaced the oil mix with TTS which I used on the Kettle and had no problems at all so would not think this this be the cause but any help would be appreciated.
Joined: Oct 03, 2005 Posts: 1595 Location: Marshall, MI
Posted: Tue Mar 29, 2011 4:45 am Post subject:
First of all whenever spark plugs get wet you might as well just replace them with new ones. Hard to tell if wet and then dryed plugs are still fouled or not. I am sure that the jet needle has a different taper to it which would change the mixture at different RPM's. Another thing to check is float level. New parts (float needle and seat, etc.) may be slightly different than original so float height may be off. Clip position of needle may help you. Take plug readings and lean the carb out until it gets better. Carbs and rich and flooding are all issues that you have to learn and figure out when owning a two stroke. _________________ You only go around once in life, but if you do it right, once is enough!
Joined: Dec 26, 2007 Posts: 1281 Location: Scottsdale, Arizona
Posted: Tue Mar 29, 2011 11:42 am Post subject: Re: 1976 GT500a Carb problem
keepemsmokin wrote:
all parts replaced on the carbs are from suzuki with there corresponding numbers as per specs/sizes but with only 2 exception the first is the Mikuni Jet Needle 5FP17-3' which is now obsolete so I replaced this with the 5FP17-5, does anyone know if these are different
Same part. The digit after the dash isn't part of the part #. It indicates the groove the clip goes in. Your clip should be in the third groove from the top.
Quote:
I have replaced the oil mix with TTS which I used on the Kettle and had no problems at all so would not think this this be the cause but any help would be appreciated.
As long as you're using that oil in the injection system, it shouldn't matter. Don't run pre mix in the tank.
Joined: Feb 22, 2011 Posts: 20 Location: UK ´Stockport´
Posted: Tue Mar 29, 2011 2:28 pm Post subject: Re: 1976 GT500a Carb problem
Bikegeezer wrote:
keepemsmokin wrote:
all parts replaced on the carbs are from suzuki with there corresponding numbers as per specs/sizes but with only 2 exception the first is the Mikuni Jet Needle 5FP17-3' which is now obsolete so I replaced this with the 5FP17-5, does anyone know if these are different
Same part. The digit after the dash isn't part of the part #. It indicates the groove the clip goes in. Your clip should be in the third groove from the top.
Hi, thankyou for this information but to be honest I'm still a little puzzled as to why they identify the jet needle with a different series '#' number for the groove position, could the taper on the #5 jet needle match up #3 if I placed the clip in the groove as stated? however since changing the jet needle and the problem i've now inherited so i have decided to take the only decent '#3' needle and the newer version '#5' and compare both dimensionlly on a shadow graph at work, hopefully this will identify any difference between them before starting alterations on the carbs as steve has said in his posting, as to the CCI oil I had my doubts on using the TTS as I've always used Bel-ray on all my 2 strokes other the years, I will keep you both posted on this issue as to I have got on. Alan
Quote:
I have replaced the oil mix with TTS which I used on the Kettle and had no problems at all so would not think this this be the cause but any help would be appreciated.
As long as you're using that oil in the injection system, it shouldn't matter. Don't run pre mix in the tank.
Joined: Dec 26, 2007 Posts: 1281 Location: Scottsdale, Arizona
Posted: Tue Mar 29, 2011 5:53 pm Post subject: Re: 1976 GT500a Carb problem
[quote="keepemsmokin"]
Bikegeezer wrote:
Hi, thankyou for this information but to be honest I'm still a little puzzled as to why they identify the jet needle with a different series '#' number for the groove position, could the taper on the #5 jet needle match up #3 if I placed the clip in the groove as stated?
Alan,
Go here for a complete explanation of Mikuni's jet needles. http://www.motorcyclecarbs.com/Mikuni_Jet_Needle_Dimension_Ch_W121C37.cfm
If it's a genuine Mikuni part. It should only have 5FP17 on it. The -5 shouldn't appear on the part. Aside from the clip position, those two needles should be identical.
FYI, the symptom you explained makes me think you might have crank seal issues.
Joined: Feb 22, 2011 Posts: 20 Location: UK ´Stockport´
Posted: Wed Mar 30, 2011 2:18 pm Post subject:
Stu
I have not been able to accurately measure the differences between the #3 and #5 jet needles until the measuring machine at work 'now broke' has been fixed, looking like next week, but what I have tried is rolling the needle's across a flat ground surface coated with micrometer blue, I have found a difference from the 3rd groove to the intersection point of the taper on both, looking at #5 needle position in relation to the original #3 from the bike then I would have to aim at positioning the clips in the 2nd groove of the #5 for a leaner mix, as to you mentioning that these should be identical then I may not have the genuine Mikuni needle as to what was purchased.
As to the crankseals could be a cause then I would agree as to being one of the main issues in the running of the old 2stroke engines having only tonight spending a little time reading up on other members problems but i've still to read a little more on procedure for checking them first, if this is my problem then I hope I can get plenty of help on this as I have never had to replace crankshaft seals before, my limitations on the engine has been top end only.
Alan
Joined: Dec 26, 2007 Posts: 1281 Location: Scottsdale, Arizona
Posted: Wed Mar 30, 2011 5:41 pm Post subject:
keepemsmokin wrote:
Stu
I have found a difference from the 3rd groove to the intersection point of the taper on both, looking at #5 needle position in relation to the original #3 from the bike then I would have to aim at positioning the clips in the 2nd groove of the #5 for a leaner mix,
Correct. Measure the distance from the #3 groove on the original needle to the beginning of the first taper. Set the clip in whatever groove on the new needle gives the same distance. Use that as a starting point, and adjust from there if necessary. Frankly, I doubt the needles are the cause of the soaked spark plugs. These carbs aren't especially hard on jet needles and needle jets, so reinstall the original parts, and see what happens.
What about float settings and float condition. Is it possible that someone blew compressed air into the fuel inlet or air screw opening of assembled carbs? That can crush the floats.
Joined: Feb 22, 2011 Posts: 20 Location: UK ´Stockport´
Posted: Sat Apr 02, 2011 10:10 am Post subject:
Firstly Id like to thank Stu and Steve for their help on this.
I now have the engine running again which was nothing to do with the carbs as i suspected, it was all down to an idiot 'actually me' draining the transmission oil using the wrong drain plug, I used the Cam Guide-Bolt thinking this was the drain plug which does not drain all the oil off, re-filling with the correct amount recommended 1400cc using a measured jug so all in all I ended up with 1700cc by mistake.
Alan
Joined: Dec 26, 2007 Posts: 1281 Location: Scottsdale, Arizona
Posted: Sun Apr 03, 2011 9:03 am Post subject:
There are two plugs to pull to completely drain the transmission oil. Regardless, over filling should only cause oil to blow out the breather. It should not be able to get into the crank chambers.
Joined: Jul 10, 2008 Posts: 1639 Location: Galveston County, Tx.
Posted: Sun Apr 03, 2011 1:52 pm Post subject:
Bikegeezer wrote:
There are two plugs to pull to completely drain the transmission oil. Regardless, over filling should only cause oil to blow out the breather. It should not be able to get into the crank chambers.
Hey Stu, allow me, in case he did not see these pics posted previously...
T and GT5500 tranny oil drain bolts Pic via Stu.jpg
Joined: Dec 26, 2007 Posts: 1281 Location: Scottsdale, Arizona
Posted: Mon Apr 04, 2011 5:37 am Post subject:
dorT500 wrote:
Bikegeezer wrote:
There are two plugs to pull to completely drain the transmission oil. Regardless, over filling should only cause oil to blow out the breather. It should not be able to get into the crank chambers.
Hey Stu, allow me, in case he did not see these pics posted previously...
LOL. The crankcase in the top pic is now in my GT500. It was a '72 case that I modified with an oil dam in the tranny and to accept the PEI ignition.
Joined: Feb 22, 2011 Posts: 20 Location: UK ´Stockport´
Posted: Mon Apr 04, 2011 11:49 am Post subject:
Thanks for these pic's I've now taken a copy and filed away in the service manual, can you confirm that the oil level screw is not an accurate measurement due to mod change's i.e. 1200/1400/1500cc changes over the years.
Had the engine running at the weekend and then will not restart. plugs still getting saturated i think this is oil as I am unable to smell petrol, I have made a few change's to the carb settings, jet needle and airscrew which made no difference what so ever so it's looks like what you said crankshaft seals or could it be worn cylinders/rings.
I have ordered a compression tester which should arrive within next couple of days before I start removing the top end, before I start this is there a way of checking the crankshaft seals while the engine is still intact.
Alan
Joined: Jul 10, 2008 Posts: 1639 Location: Galveston County, Tx.
Posted: Mon Apr 04, 2011 2:39 pm Post subject:
keepemsmokin wrote:
...... confirm that the oil level screw is not an accurate measurement due to mod change's i.e. 1200/1400/1500cc changes over the years?
Oh yeah, disregard the oil level screw. You can just make a dipstick out of a narrow piece of coil stock with a 90 degree bend in it to rest on top of the filler hole when checking your oil level. I happened to make one out of a piece of stainless steel half inch wide coil stock and just snipped a small notch where the oil level was after draining the oil completely from both drain plugs and refilling with 1400 ccs. I carry the dipstick in a tool bag on the bike. _________________ _________________________________
GONE.......WITH A PUFF OF SMOKE AND A BLUR OF SPOKE........
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