12KLX250S all mods, more power without big bore??
#1
02-10-2019, 04:06 PM
12KLX250S all mods, more power without big bore??
2012 KLX250S, FMF powerbomb/Q4, all carb mods, one tooth smaller countershaft sprocket, air lid removed/twinair.
Has anyone tried other cams, polish/porting for a little more power? I talked to a really good service tech about big bore, bill blue.
He said mixed reviews, vibration, and other issues, he himself as a rider would not go big bore.
My bike runs stellar, but I would just like to squeeze a bit more power out of it without making it unreliable. I ride alone a lot in the Colorado woods on seldom ridden trails.
I got a name from him of a guy that builds flat track racers, with a dyno, just curious if others have taken the stock motor and got more out of it reliably. The guy has a stellar reputation.
At this point I am not looking to go big bore at all, looking for alternatives.
Has anyone tried other cams, polish/porting for a little more power? I talked to a really good service tech about big bore, bill blue.
He said mixed reviews, vibration, and other issues, he himself as a rider would not go big bore.
My bike runs stellar, but I would just like to squeeze a bit more power out of it without making it unreliable. I ride alone a lot in the Colorado woods on seldom ridden trails.
I got a name from him of a guy that builds flat track racers, with a dyno, just curious if others have taken the stock motor and got more out of it reliably. The guy has a stellar reputation.
At this point I am not looking to go big bore at all, looking for alternatives.
#2
02-10-2019, 06:11 PM
Apparently you have not done the MCM ( Marcelino Cam Mod) ? That is the mod you should have done first - especially for high altitude performance.. After you complete the MCM, you will have a significant increase in power - and all the power possible with DIY stockbore mods - then you will be able to correctly determine if you need more...
I assume you are running the "full exhaust system lidless CVK setup" , and you've properly rejetted for your altitudes.
I assume you are running the "full exhaust system lidless CVK setup" , and you've properly rejetted for your altitudes.
Last edited by Klxster; 02-10-2019 at 06:16 PM.
#3
02-10-2019, 08:38 PM
FWIW...
When I was selling bikes I used to be anti-big bore, but after boring my KLX650 over 2mm I learned it was no different than a normal top end job and totally reliable, 30,000 miles and still strong. I bought one of the Chinese AHL 299cc kits to do my 250 due to the pricing being under $200 and a bolt on with a minor bit of grinding on the lower spring tensioner cap. The only negative I've ever heard of that was true for all 351s was the slightly lower water jacket volume around the cylinder. In the ADVrider forum there is a rider who had 115,000+ miles on a 351 over in Thailand. Fact is I'd do a big bore before cams just due to the tractability and reliability of a properly assembled big bore. The big bore usually adds more power over the entire rpm range, maybe slightly reducing the peak rpm, but any drop can be easily recovered by stepping up the gearing allowed by the added power.
The balance factor relative to a single isn't much of an issue. Vibration is probably more an issue on individual bike by bike case since the factory doesn't bother with any serious balancing. I also asked a late friend, machinist, and former dealership mechanic about his punched out drag bike, he said he'd loved to have balanced the engine, but the money was better spent on other stuff first. He was a record holder with his H2 triple and was running a big bore in-line 4 after that. No other mechanics at the dealership discouraged me and one was the instigator with the big bore KLX650, having found the wrist pin fit in both pistons and the decks appeared to be very close to the same on a Vulcan 1500 piston. I measured it up and it was a bolt in with a bore job and the head gasket trimmed to the larger ID.
I, personally, am on board with big bores. The only negative is the cost for multi-cylinders, not so much for singles. Even my SR500 is a big bore with a 528cc set up.
When I was selling bikes I used to be anti-big bore, but after boring my KLX650 over 2mm I learned it was no different than a normal top end job and totally reliable, 30,000 miles and still strong. I bought one of the Chinese AHL 299cc kits to do my 250 due to the pricing being under $200 and a bolt on with a minor bit of grinding on the lower spring tensioner cap. The only negative I've ever heard of that was true for all 351s was the slightly lower water jacket volume around the cylinder. In the ADVrider forum there is a rider who had 115,000+ miles on a 351 over in Thailand. Fact is I'd do a big bore before cams just due to the tractability and reliability of a properly assembled big bore. The big bore usually adds more power over the entire rpm range, maybe slightly reducing the peak rpm, but any drop can be easily recovered by stepping up the gearing allowed by the added power.
The balance factor relative to a single isn't much of an issue. Vibration is probably more an issue on individual bike by bike case since the factory doesn't bother with any serious balancing. I also asked a late friend, machinist, and former dealership mechanic about his punched out drag bike, he said he'd loved to have balanced the engine, but the money was better spent on other stuff first. He was a record holder with his H2 triple and was running a big bore in-line 4 after that. No other mechanics at the dealership discouraged me and one was the instigator with the big bore KLX650, having found the wrist pin fit in both pistons and the decks appeared to be very close to the same on a Vulcan 1500 piston. I measured it up and it was a bolt in with a bore job and the head gasket trimmed to the larger ID.
I, personally, am on board with big bores. The only negative is the cost for multi-cylinders, not so much for singles. Even my SR500 is a big bore with a 528cc set up.
Last edited by klx678; 02-10-2019 at 09:18 PM.
#4
02-10-2019, 09:34 PM
I've owned a '12S since 2013. Did the basic suspension/gearing mods first with good results. Engine suffered a rod bearing failure @12k so I decided to go all in. 351, Web cam and some port work. I am a mechanic/machinist so I have plenty of experience porting heads. Based on what I found with the head casting, it isn't suitable for flowing good numbers even with a lot of work. Best bang for the buck is added displacement. It allows the engine to produce better torque at lower engine speeds so wear should be reduced. The only thing I think that Bill should incorporate into his kit would be adding a dry film coating on the piston skirts.
The 101 cams added a bit of over-run but for the expense, I wouldn't bother if I had it all to do again. Reliability is just as good as OE, just be thorough when assembling.
The 101 cams added a bit of over-run but for the expense, I wouldn't bother if I had it all to do again. Reliability is just as good as OE, just be thorough when assembling.
Last edited by GBAUTO; 02-10-2019 at 09:39 PM.
#5
02-11-2019, 12:39 AM
OP, the mods you performed don't usually add a bunch of power, but what they do accomplish is that the extra power you do attain is across a wider section of the power band, along with noticeably better throttle response.
The old adage that "there's no replacement for displacement" is pretty much true. It yields the most beneficial return. Even the factory 300 jug I put on mine was worth it, and Bill's and other bigger bore setups are even better.
I tend to disagree with your source's assessment on bigger bores. Unless the kit is poor or the installation is botched, 4-stroke motorcycles and just about everything else responds very positively to more displacement.
The old adage that "there's no replacement for displacement" is pretty much true. It yields the most beneficial return. Even the factory 300 jug I put on mine was worth it, and Bill's and other bigger bore setups are even better.
I tend to disagree with your source's assessment on bigger bores. Unless the kit is poor or the installation is botched, 4-stroke motorcycles and just about everything else responds very positively to more displacement.
#6
04-15-2020, 01:32 PM
FWIW...
When I was selling bikes I used to be anti-big bore, but after boring my KLX650 over 2mm I learned it was no different than a normal top end job and totally reliable, 30,000 miles and still strong. I bought one of the Chinese AHL 299cc kits to do my 250 due to the pricing being under $200 and a bolt on with a minor bit of grinding on the lower spring tensioner cap. The only negative I've ever heard of that was true for all 351s was the slightly lower water jacket volume around the cylinder. In the ADVrider forum there is a rider who had 115,000+ miles on a 351 over in Thailand. Fact is I'd do a big bore before cams just due to the tractability and reliability of a properly assembled big bore. The big bore usually adds more power over the entire rpm range, maybe slightly reducing the peak rpm, but any drop can be easily recovered by stepping up the gearing allowed by the added power.
The balance factor relative to a single isn't much of an issue. Vibration is probably more an issue on individual bike by bike case since the factory doesn't bother with any serious balancing. I also asked a late friend, machinist, and former dealership mechanic about his punched out drag bike, he said he'd loved to have balanced the engine, but the money was better spent on other stuff first. He was a record holder with his H2 triple and was running a big bore in-line 4 after that. No other mechanics at the dealership discouraged me and one was the instigator with the big bore KLX650, having found the wrist pin fit in both pistons and the decks appeared to be very close to the same on a Vulcan 1500 piston. I measured it up and it was a bolt in with a bore job and the head gasket trimmed to the larger ID.
I, personally, am on board with big bores. The only negative is the cost for multi-cylinders, not so much for singles. Even my SR500 is a big bore with a 528cc set up.
When I was selling bikes I used to be anti-big bore, but after boring my KLX650 over 2mm I learned it was no different than a normal top end job and totally reliable, 30,000 miles and still strong. I bought one of the Chinese AHL 299cc kits to do my 250 due to the pricing being under $200 and a bolt on with a minor bit of grinding on the lower spring tensioner cap. The only negative I've ever heard of that was true for all 351s was the slightly lower water jacket volume around the cylinder. In the ADVrider forum there is a rider who had 115,000+ miles on a 351 over in Thailand. Fact is I'd do a big bore before cams just due to the tractability and reliability of a properly assembled big bore. The big bore usually adds more power over the entire rpm range, maybe slightly reducing the peak rpm, but any drop can be easily recovered by stepping up the gearing allowed by the added power.
The balance factor relative to a single isn't much of an issue. Vibration is probably more an issue on individual bike by bike case since the factory doesn't bother with any serious balancing. I also asked a late friend, machinist, and former dealership mechanic about his punched out drag bike, he said he'd loved to have balanced the engine, but the money was better spent on other stuff first. He was a record holder with his H2 triple and was running a big bore in-line 4 after that. No other mechanics at the dealership discouraged me and one was the instigator with the big bore KLX650, having found the wrist pin fit in both pistons and the decks appeared to be very close to the same on a Vulcan 1500 piston. I measured it up and it was a bolt in with a bore job and the head gasket trimmed to the larger ID.
I, personally, am on board with big bores. The only negative is the cost for multi-cylinders, not so much for singles. Even my SR500 is a big bore with a 528cc set up.
May i ask how many miles you currently have on the ahl kit.
Still happy with the quality?
I am checking to buy one myself.
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