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TOPIC: Re:Tuning Woes: Cam, not Carb
#1019641
Bradspeedstar (User)
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Tuning Woes: Cam, not Carb 4 Days, 22 Hours ago  
Hey folks,
I've been bugging you all (particularly Davej) for some time about my part throttle tuning woes. I've tried all the suggestions to go leaner and richer to no avail. Yesterday I think I hit upon the actual source of my problem: my intake/carb/cam/exhaust combo. Here's the whole story, to the best of my knowledge, please bear with me. I'm no engine builder nor am I an expert mechanic.

According to service records, my bike was fitted with the entire Speed Star Stage IV kit a decade ago, minus the intake and exhaust. The PO ran a K&N on stock backing plate and Bub Stubbies. I'm guessing the Stubbies are the reason he opted for the smaller HSR42 instead of the HSR45 that comes with the full kit. This is why I always assumed it had the bigger one. Whoops. The next owner rebuilt the engine (it scattered a piston at some point) and threw a Pro Pipe HS on it, and sold it to me with a dropped lifter, dead battery, and broken air cleaner on it, tuned 32 pilot 97 needle 3rd notch and 160 main.

Once I repaired it all and threw a xXx air cleaner on it, I realized it made a gnarly noise while cruising low throttle positions, sounding like the stumble you get when you roll off with a rich setting. It was persistent at the throttle opening I used for cruising and decelerating, from just off idle to 1/4 throttle. I assumed, until yesterday, that it was a rough spot from tuning. It can't be, though, because I've run every size jet and needle I could think of and it doesn't affect it whatsoever. in fact, at any pilot size 25 and up it loads up at idle.

I think that it's due to my setup. Here's why.
-My idle lopes a lot. the rough running down low is probably lope too. The speed star cams have a lot of overlap due to late closing exhaust and early opening intake, which makes for a rough idle and rough low end performance. The intake opens at 11* BTDC and the exhaust closes at 15* ATDC.
-I can hear my slide making noise at idle too, because the reversion pulse of the exhaust flowing through the intake at idle makes the slide click against the carb body.
-Opening up the throttle makes the roughness go away, but if you hold the throttle at a set point below 1/4 or so it starts to lope again.

I know it's the nature of a cam with a lot of overlap, but there's gotta be a way to make it a little more driveable. I pulled the baffle out of the pipe yesterday and found all the packing was blown out. When you run it without the baffle, the reversion is worse because of the lack of back pressure. I put a few hose clamps over holes in the baffle, essentially restricting airflow to give it some pressure. The bike responded great to this as far as torque goes, but the lopey reversion thing is still present.

Thanks for making it through this longwinded post. Here's what I'm left with: Is my diagnosis correct? Can I fix it? Maybe try the proper HSR45 carb, or a different pipe? Different intake? Is it just the cam? Would it be worth it to have a set of Warrior cams ground to fit in my bike instead because they have less overlap? What can I do? Is there a way to tune it out of the bike at all with carburetion?

Thanks to everyone that has helped me, I know I ask a lot of you.
 
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#1019654
SKWEARpeg (User)
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Re:Tuning Woes: Cam, not Carb 4 Days, 19 Hours ago  
The idle needs to be at about 900rpms. If it's not there, turn it up. These bikes will idle as low as 600rpms when they're hot. Resist the temptation to think its okay. There's a 45 pound crank buried inside the motor. When the idle is set correctly, it is always making forward progress. You turn the idle to low, and the crank starts more of a jerky motion. Maybe you want that, but I wouldn't. It causes premature wear of lots of important stuff...of which egos are not one of.

My thought is they used the 42, because a 40 is plenty big for the motor. A 45 is actually on the big side for these bikes. There's only so much air you can suck into a cylinder(s). You want the correct air fuel mix. If you go to big on the carb...ie a 45, you're moving more air, and would need to compensate with extra fuel to avoid being lean, especially at the top end as far as speeds and WOT when your moving the most air. These carbs a re a simple afair, and they are constantly struggling for a compromise.
 
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#1019707
dave377 (User)
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Re:Tuning Woes: Cam, not Carb 3 Days, 22 Hours ago  
Make sure you don.t have a vac. leak. Check real good around the intake to head area and the intake to carb and make sure vac port on top of the intake is plugged . Mine was leaking at the intake to carb and it kind of acted like yours just not as bad.

Good luck
Dave377
 
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#1019711
Ctkog (User)
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Re:Tuning Woes: Cam, not Carb 3 Days, 21 Hours ago  
any intake cracks that have broken thru?
 
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#1019713
Bradspeedstar (User)
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Re:Tuning Woes: Cam, not Carb 3 Days, 20 Hours ago  
It idles at 900, yes. With the semi-radical cam it doesn't enjoy any less anyway.

The carb specified for my mods is the 45. The only reason to run less in my mind is because they had short 2-2 pipes and basically a stock intake as opposed to the race-tuned pipes specified and the billet air cleaner plate etc. The 42 is for the stage 3 kit which doesn't run the cam or valve train work. Makes me wonder if running the 45 now that I improved the intake and exhaust situation would free flow up and help with the reversion.

I replaced my intake manifold and orings this year because the old one looked pretty rough/weathered/cracked. When I checked around with just a can of carb cleaner it indicated a leak no matter what I did, but the mechanic I spoke with at the dealer made a good point: that fine mist can and will suck around into the air cleaner. He said only use water. Water indicated no leak.

I haven't scrutinized the carb to intake part much though Dave, I guess I'll take a look there next. All the dousing in the world never affected idle from the manifold to head seals though.

I'm inclined to think that this is resultant of my cam characteristics. My brother's Vmaxx was kinda like this, and the other guy I found in a Web search with this issue was running a 585 cam on a twin cam Harley, which is in the same ballpark for overlap.
 
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Last Edit: 2017/08/13 11:55 By Bradspeedstar.
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#1019721
pastornj (User)
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Re:Tuning Woes: Cam, not Carb 3 Days, 17 Hours ago  
This won't solve all of your problems, but a pair of torque cones - I picked some up on eBay for $12.82 from sampowersports1 for a HD EVO - will help a lot with the short pipes and weak low end.

If the cams are a problem I would go back to stock or get a set from Patrick racing. Too much overlap on a low rpm motor will never work well.

NJ
 
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#1019722
Bradspeedstar (User)
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Re:Tuning Woes: Cam, not Carb 3 Days, 17 Hours ago  
Pastornj, what cam are you running on your big bore? I didn't see mention of it on your profile. I dig your setup.
 
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#1019725
Bradspeedstar (User)
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Re:Tuning Woes: Cam, not Carb 3 Days, 16 Hours ago  
 
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#1019726
Bradspeedstar (User)
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Re:Tuning Woes: Cam, not Carb 3 Days, 16 Hours ago  
video 2
I just took these videos of my bike, you can hear the sound when it's sitting but it is a little different when it's running rough like that under load. Idle is 850-900 rpm.
 
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#1019728
Curt (Moderator)
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Re:Tuning Woes: Cam, not Carb 3 Days, 16 Hours ago  
My jetting is for a 45 on a stock bore 1700. I think you can jet better. Go down load the tuning manual for the Mikuni HSR carbs and read thru it goo. here is the link. Do you have the TPS mod done to the HSR? If not the I have the documentation on how to do it. PM me your e-mail address if you want any of my documentation I had on my site.

http://www.mikuni.com/fs-tuning_guide.html

http://www.mikuni.com/fs-performance_guide.html
 
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