SP carbs on non SP motor?

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4hundread
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SP carbs on non SP motor?

Post by 4hundread » Wed Mar 28, 2018 11:22 am

Anyone able to offer any advice on this, as far as I'm aware the only differences are obviously the bore of the carbs, TPS which is not an issue and the bigger needle jet and needle.

I have just rebuilt a set with litetek seals, the whole lot, throttle shaft seals and all. I set the needles on the middle clip and the mixture screws 2 turns out. Starts perfectly and she will take a rev all be it a wee bit wooly around the 5k mark.

I am running a k & n air filter with what I think is the small hole rubber (it was on the bike when I got it so nothing to compare with), Sandys downpipes with an unknown link pipe that has the standard step down to 38mm and a Micron end can.

I know a dyno trip will be in order, but wondered if anyone had a ballpark setup.

Cheers, si

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SevenThreeSeven
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Re: SP carbs on non SP motor?

Post by SevenThreeSeven » Wed Mar 28, 2018 2:04 pm

The only thought that comes to mind on this endeavor is "what about the ignition timing?"

(IIRC) The SP had an Ignition control module with inputs for coolant temperature and the Throttle Position Sensor. The SP model of the GSXR, being more of a racing tuned engine, was set up to run maximum horsepower and/or torque air-fuel ratios at higher RPMs for more top end power, which explains the different carbs and their jetting. This made the RPMs between idle and the targeted high-RPM horsepower a bit of a delicate balancing act. The coolant temp and TPS inputs to the ignition control gave the engine more active and fine-tuned spark advance which helped the engine to get past (to be able to rev properly through) the parts of its operating envelope between idle and wide open throttle.

Of course, with changes to the exhaust and intake on your particular bike it's possible that the entire equation that the SP's original ignition control wouldn't exactly apply to your situation. Maybe more efficiency in airflow through the cylinders will make it possible for SP carbs to work well with a non-SP ignition control box (by making idle and midrange RPM situations slightly more lean).

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Re: SP carbs on non SP motor?

Post by 4hundread » Wed Mar 28, 2018 5:24 pm

SevenThreeSeven wrote:The only thought that comes to mind on this endeavor is "what about the ignition timing?"

(IIRC) The SP had an Ignition control module with inputs for coolant temperature and the Throttle Position Sensor. The SP model of the GSXR, being more of a racing tuned engine, was set up to run maximum horsepower and/or torque air-fuel ratios at higher RPMs for more top end power, which explains the different carbs and their jetting. This made the RPMs between idle and the targeted high-RPM horsepower a bit of a delicate balancing act. The coolant temp and TPS inputs to the ignition control gave the engine more active and fine-tuned spark advance which helped the engine to get past (to be able to rev properly through) the parts of its operating envelope between idle and wide open throttle.

Of course, with changes to the exhaust and intake on your particular bike it's possible that the entire equation that the SP's original ignition control wouldn't exactly apply to your situation. Maybe more efficiency in airflow through the cylinders will make it possible for SP carbs to work well with a non-SP ignition control box (by making idle and midrange RPM situations slightly more lean).
I'm sure the bike had a similar fluff in the fueling on the standard 33mm carbs, but it's been 18 months since I last rode it.

I am hoping to take it for an MOT in the next couple of weeks so will see how it fuels on the road, if it's just a wee flat spot and pulls cleanly everywhere else I may live with it. I don't mind doing a couple of runs on the dyno just to check it doesn't go horribly weak anywhere but I'm not inclined to spend hours on the dyno and a fortune on jets.

I still have the standard carbs if it's really not happy, may be a case of doing the seals in them too and refitting them. Probably should have just left it standard but where's the fun in that.

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moforockband
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Re: SP carbs on non SP motor?

Post by moforockband » Wed Mar 28, 2018 10:12 pm

YO! It will be unfortunately the headers you have that will be causing the hole going from what I've read previously. These little 400's need smooth uninterrupted airflow through the intake and exhaust to get perfect carburation. The stock headers are excellent at making the bike smooth.
I've found by increasing the diameter of the headers and removing baffles/sticking race cans on etc etc you get a couple more ponies, but get holes in the power delivery.
But I really don't care as I came from 2 strokes, and I'm used to crazy power delivery!

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Re: SP carbs on non SP motor?

Post by 4hundread » Wed Mar 28, 2018 11:28 pm

moforockband wrote:YO! It will be unfortunately the headers you have that will be causing the hole going from what I've read previously. These little 400's need smooth uninterrupted airflow through the intake and exhaust to get perfect carburation. The stock headers are excellent at making the bike smooth.
I've found by increasing the diameter of the headers and removing baffles/sticking race cans on etc etc you get a couple more ponies, but get holes in the power delivery.
But I really don't care as I came from 2 strokes, and I'm used to crazy power delivery!
Aye, I am aware of the issues with the Sandys headers and am seriously thinking about getting balance pipes welded in as per the factory pipes to see if this improves things. It was on my to do list but the bike has been sidelined for a fair while.

Will give it a blast on the road and see what like, can live with a wee fluff as long as it's as reliable as it used to be.

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moforockband
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Re: SP carbs on non SP motor?

Post by moforockband » Wed Mar 28, 2018 11:47 pm

4hundread wrote:
Wed Mar 28, 2018 11:28 pm
moforockband wrote:YO! It will be unfortunately the headers you have that will be causing the hole going from what I've read previously. These little 400's need smooth uninterrupted airflow through the intake and exhaust to get perfect carburation. The stock headers are excellent at making the bike smooth.
I've found by increasing the diameter of the headers and removing baffles/sticking race cans on etc etc you get a couple more ponies, but get holes in the power delivery.
But I really don't care as I came from 2 strokes, and I'm used to crazy power delivery!
Aye, I am aware of the issues with the Sandys headers and am seriously thinking about getting balance pipes welded in as per the factory pipes to see if this improves things. It was on my to do list but the bike has been sidelined for a fair while.

Will give it a blast on the road and see what like, can live with a wee fluff as long as it's as reliable as it used to be.

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Check the id of your sandy pipes 1st. 29mm iirc on std 73a pipes, and bandit 400. Many Suzuki collectors (ie bandit 400) have a baffle tube welded in the collector to speed gas flow up through the system to help low rpm running. I had my set gutted, to boost hp at the top.

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Re: SP carbs on non SP motor?

Post by 4hundread » Thu Mar 29, 2018 12:02 am

moforockband wrote:
4hundread wrote:
Wed Mar 28, 2018 11:28 pm
moforockband wrote:YO! It will be unfortunately the headers you have that will be causing the hole going from what I've read previously. These little 400's need smooth uninterrupted airflow through the intake and exhaust to get perfect carburation. The stock headers are excellent at making the bike smooth.
I've found by increasing the diameter of the headers and removing baffles/sticking race cans on etc etc you get a couple more ponies, but get holes in the power delivery.
But I really don't care as I came from 2 strokes, and I'm used to crazy power delivery!
Aye, I am aware of the issues with the Sandys headers and am seriously thinking about getting balance pipes welded in as per the factory pipes to see if this improves things. It was on my to do list but the bike has been sidelined for a fair while.

Will give it a blast on the road and see what like, can live with a wee fluff as long as it's as reliable as it used to be.

Sent from my SM-A510F using Tapatalk
Check the id of your sandy pipes 1st. 29mm iirc on std 73a pipes, and bandit 400. Many Suzuki collectors (ie bandit 400) have a baffle tube welded in the collector to speed gas flow up through the system to help low rpm running. I had my set gutted, to boost hp at the top.
The factory headers just had a vertical plate at the rear of the collector where the link pipe joins. Both the factory end can and the current link pipe are 38mm at the joint to the headers, header outlet is 45mm. I know Rover used a step in the pipework of the manifolds on the k series to help plump up the midrange.

I will keep an eye out for a decent set of factory headers, mine were rotten and the Sandys pipes came up at the right money, if I had bought them new and paid full price for them i would have been very disappointed.

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Re: SP carbs on non SP motor?

Post by 4hundread » Sun Apr 15, 2018 6:31 pm

4hundread wrote:
moforockband wrote:
4hundread wrote:
Wed Mar 28, 2018 11:28 pm
Aye, I am aware of the issues with the Sandys headers and am seriously thinking about getting balance pipes welded in as per the factory pipes to see if this improves things. It was on my to do list but the bike has been sidelined for a fair while.

Will give it a blast on the road and see what like, can live with a wee fluff as long as it's as reliable as it used to be.

Sent from my SM-A510F using Tapatalk
Check the id of your sandy pipes 1st. 29mm iirc on std 73a pipes, and bandit 400. Many Suzuki collectors (ie bandit 400) have a baffle tube welded in the collector to speed gas flow up through the system to help low rpm running. I had my set gutted, to boost hp at the top.
The factory headers just had a vertical plate at the rear of the collector where the link pipe joins. Both the factory end can and the current link pipe are 38mm at the joint to the headers, header outlet is 45mm. I know Rover used a step in the pipework of the manifolds on the k series to help plump up the midrange.

I will keep an eye out for a decent set of factory headers, mine were rotten and the Sandys pipes came up at the right money, if I had bought them new and paid full price for them i would have been very disappointed.

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Nowt to do with the carbs, just a pic of a clean front end.Image

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