Hot start issues. Any ideas? - Suzuki GSX-R Motorcycle Forums Gixxer.com
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post #1 of 16 (permalink) Old 08-08-2018, 03:40 AM Thread Starter
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Hot start issues. Any ideas?

Tried the search function but for some reason only shows results for 2018

Anyway, finally finished the build and fired it up. Cold start isn't great but I've got it down to having to twist the throttle 3 or 4 times, pull the choke and usually it will start after a couple of goes. Idle mixture is slightly on the rich side. Once it's warmed up. it's an absolute ball tearer, no flatspots and idles well.

Problem is. once I shut it down. it's very difficult to restart. I've tried the idle mixture from slightly rich to lean which doesn't seem to help. I've tried starting with no throttle to slowly opening the throttle, pumping the throttle, slamming shut the throttle but nothing seems to work. I've checked the tank breather which is fine. Spark plugs look slightly rich but not enough to be an issue.

Engine has a weaker than normal crank speed due to the high comp and kicks back a bit when it doesn't fire. Also has a 4 degree advancer

My other 7/11 had a very weak crank and would struggle to start but since converting to 24v start . it's been perfect since. Difference is, it wouldn't start cold or hot which leads me to believe it's a different issue with the new bike

Any ideas appreciated
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post #2 of 16 (permalink) Old 08-11-2018, 12:01 AM
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Re: Hot start issues. Any ideas?

Slow crank & dirty plugs would definatley not help one bit, is this with a full charged & good battery and slow crank is only due to high comp ??
What type of carbie is fitted ?
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post #3 of 16 (permalink) Old 08-11-2018, 01:14 AM Thread Starter
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Re: Hot start issues. Any ideas?

Yes, battery brand new and fully charged. Comp is 12:1 and carbies are TMR40's.

I might swap out the advancer but I have a feeling it's the high comp creating the slow crank which then makes it hard to fire when hot. There isn't much difference in crank speed from cold to hot
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post #4 of 16 (permalink) Old 08-12-2018, 06:23 PM
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Re: Hot start issues. Any ideas?

"Mikuni TMR" nice carbs, "40s" Im guessing these are on your 1100 bike ?
What made you choose Mikuni TMR over the Mikuni RS carbs ?
Just realized 7/11 (750 frame / 1100 motor)

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post #5 of 16 (permalink) Old 08-13-2018, 12:27 AM
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Re: Hot start issues. Any ideas?

New big bore rings create a lot more friction for a few miles (and heat) - my LiFeO4 battery has more cranking power than lead acid./gel and had no problem spinning the engine over after big bore, then still having enough current to provide a strong spark. I reckon that's what it is, battery doesn't have extra strength to supply current for coils whilst cranking ...… the kicking back seems to confirm this - this can crack the starter gear and cause damage
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post #6 of 16 (permalink) Old 08-13-2018, 01:27 AM Thread Starter
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Re: Hot start issues. Any ideas?

Quote:
Originally Posted by 91OilCooled View Post
"Mikuni TMR" nice carbs, "40s" Im guessing these are on your 1100 bike ?
What made you choose Mikuni TMR over the Mikuni RS carbs ?
Just realized 7/11 (750 frame / 1100 motor)
Came across the TMR's at a decent price so couldn't refuse. I have RS40's on one 7/11 and TMR40's on my other 7/11. Engines are similar in capacity, head mods, etc, except that the TMR engine has hotter cams. Overall the TMR engine feels more responsive and aggressive but that's because of a combination of several factors
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post #7 of 16 (permalink) Old 08-13-2018, 01:34 AM Thread Starter
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Re: Hot start issues. Any ideas?

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Originally Posted by nickr View Post
New big bore rings create a lot more friction for a few miles (and heat) - my LiFeO4 battery has more cranking power than lead acid./gel and had no problem spinning the engine over after big bore, then still having enough current to provide a strong spark. I reckon that's what it is, battery doesn't have extra strength to supply current for coils whilst cranking ...… the kicking back seems to confirm this - this can crack the starter gear and cause damage
It tend to agree. I've order a second battery for 24v starting mod.
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post #8 of 16 (permalink) Old 08-13-2018, 06:36 PM
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Re: Hot start issues. Any ideas?

Quote:
Originally Posted by 64george View Post
Came across the TMR's at a decent price so couldn't refuse. I have RS40's on one 7/11 and TMR40's on my other 7/11. Engines are similar in capacity, head mods, etc, except that the TMR engine has hotter cams. Overall the TMR engine feels more responsive and aggressive but that's because of a combination of several factors
Wow very tidy set up, great to see.
So much room in an 1100 engine, with my RS36 carbs on the 750 the two middle float bowls basically sit on the alternator - pain in the arse you cant even change the main jets without removing.
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post #9 of 16 (permalink) Old 08-14-2018, 03:38 AM Thread Starter
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Re: Hot start issues. Any ideas?

Quote:
Originally Posted by 91OilCooled View Post
Wow very tidy set up, great to see.
So much room in an 1100 engine, with my RS36 carbs on the 750 the two middle float bowls basically sit on the alternator - pain in the arse you cant even change the main jets without removing.
Thanks, I'm really happy with the result. Just need to sort the hot start issue and I might even register this one
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post #10 of 16 (permalink) Old 08-14-2018, 05:47 PM
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It tend to agree. I've order a second battery for 24v starting mod.
Not sure what batteries you are using but Ive changed to Lithium Batteries, they are called SSB Power Sport.
They are light and have extra crank power, best thing is they dont go flat when your not using them, they can sit disconnected for 12 months and still be 100 percent.
Im using a SSB LH7B-4 it has 180CCA weighs 0.8kg so two of these batteries would still weigh less than a standard battery, it cost $130 3 years ago and hasn't missed a beat - haven't even done a top up charge.
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post #11 of 16 (permalink) Old 08-15-2018, 02:25 AM Thread Starter
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Re: Hot start issues. Any ideas?

Quote:
Originally Posted by 91OilCooled View Post
Not sure what batteries you are using but Ive changed to Lithium Batteries, they are called SSB Power Sport.
They are light and have extra crank power, best thing is they dont go flat when your not using them, they can sit disconnected for 12 months and still be 100 percent.
Im using a SSB LH7B-4 it has 180CCA weighs 0.8kg so two of these batteries would still weigh less than a standard battery, it cost $130 3 years ago and hasn't missed a beat - haven't even done a top up charge.
I put a SSB lithium 290cca in the black and silver 7/11 and still had to convert to 24v. Compression is high in that bike. Close to 13

In the new build same story, 290cca and just not up to it. Comp is around 12

Going to end up with enough batteries to power a small town soon
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post #12 of 16 (permalink) Old 08-16-2018, 01:12 AM
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Re: Hot start issues. Any ideas?

Yeah I saw the 290cca thats a lot of crank for a small battery, cant believe thats not big enough - 24v it is then I guess I hope that fixes your problem.
You might have to look into how these new bikes start.
I know the new 2018 model GSXRs have high comp i wonder what theve done to get them to start so easy ??
The 750 has a compression ratio of 12.5:1
The 1000 has a compression ratio of 13.2:1
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post #13 of 16 (permalink) Old 08-16-2018, 03:46 AM Thread Starter
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Re: Hot start issues. Any ideas?

Been wondering that myself.... with half the size starters also!
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post #14 of 16 (permalink) Old 08-16-2018, 07:00 AM
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Re: Hot start issues. Any ideas?

Just been thinking (always dangerous !)
A big bore engine (1186/1216) with 12:1 compression should be fine with a single uprate battery - are ring gaps too small ? starter motor needs over-haul ? It's normally only the big block engines that need 24v at high compression levels.
The modern engines with 13:1 or so compression have more radical cams than ours, so static compression (or low speed cranking) - more over-lap effectively reduces compression. High speed dynamic compression will be higher - that's my understanding of it - plus 1000's have a smaller cylinder.
I use 280 cca JMT batteries in a couple of my bikes, always spin quick enough. Have seen a few starter idler gears causing expensive damage due to slow cranking kick back incidents - the early Hayabusa's were prone to this with a weak battery, latter ones had a starter clutch that free-wheeled if this happened - so if it's slow definitely take measures !
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post #15 of 16 (permalink) Old 08-16-2018, 04:30 PM
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Re: Hot start issues. Any ideas?

Had same problem with my -87 7/11. (1255 Wiseco bb-kit 13,5:1 comp., CR38 carbs, and ign.advancer.)
My solution is high octane fuel (98) and octane booster on top.
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post #16 of 16 (permalink) Old 08-23-2018, 02:07 AM Thread Starter
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Re: Hot start issues. Any ideas?

Problem solved!

24v in both my 7/11's now. Much improved cold start also. Only need to hold choke on and hit start. Hot start, tiny touch of the throttle with the start switch and she's running.

Just need to sort out an oil catch tank and some suitable mirrors and it's 100% completed.....for now anyways
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