Hi:
My question is not strictly about FJs, but it is for a carburated bike, my CBX 750, so I think it could be useful
The bike runs great and sweet, but It has a hole in the power-band between 5000 to 7000 rpm. It is uncomfortable, much more after riding my FJ.
I think I have to raise the needles to give more fuel, but I´m not sure, because the bike runs the same hot or cold. I think it is due to the Mac exhaust design, but I can´t come back to the mild steel rotten OE exhausts and collectors
Settings: Dynojet kit as spec, except that running Keihin OE 115 main instead the DJ main (tested a lot of mains and this is the best main jet), Mac 4/1 exhaust (race) and KN filter
Ok, I know that I have only 2 possibilities (needles up or down), but I´m sure that the Murphy Law says that if I change anything I´m going to make the wrong way, so I would like to know your advices
Best regards
Alf
My understanding of jetting is throttle opening, not rpm determine what circuit of the carb you are using. What % of throttle are you at when this happens? When was the last time the carbs were synced?
Kurt
Hola, Kurt
1/2 to full throttle. The effect is greater as faster you open the throttle. If you´re progressive with the opening the effect diminished.
And pasing that zone, from 7500 onwards, the acceleration is like a turbo is engaged (well, I´m exaggerating for a 70-80 hp air-cooled engine, but really is so fast there)
Sync is not the problem
Thanks
4-1 exhausts will always have a hole in the power someplace.
Shove the needles around and you may be able to minimize it some, but it'll still exist.
Try to raise the needles one notch, richer mixture. See if this helps.
Kurt
Thanks, Kurt
In fact that´s the movement that probably I will do, mainly for precaution (you know, if the bike runs too lean, it breaks), but only 1/2 notch with a shim, but It could bee too the bike is running rich between 5-7000 rpm :wacko2:
Quote from: Alf on September 16, 2012, 11:29:17 AM
Thanks, Kurt
In fact that´s the movement that probably I will do, mainly for precaution (you know, if the bike runs too lean, it breaks), but only 1/2 notch with a shim, but It could bee too the bike is running rich between 5-7000 rpm :wacko2:
Alf I think you are on the right path. Like Andy said you just half to try is and see what it happens. The fun of trial and error. Hope this helps.
Kurt
Didn't DynoJet do something with the air jets to remove the flat spot in the FJ?
[/quote]Alf I think you are on the right path. Like Andy said you just half to try is and see what it happens. The fun of trial and error. Hope this helps.
Kurt
[/quote]
Have you dismantled a CBX 750 carbs?. Well, the fun finish when you have to refit the airbox ducts to the carbs. The best mark that I´ve got (after boil the ducts in my kitchen and get sleep a night in my armchair after my wife discovered me) was 1 and half hours!! Horrible, really!
Quote from: andyb on September 16, 2012, 08:33:00 AM
4-1 exhausts will always have a hole in the power someplace.
Shove the needles around and you may be able to minimize it some, but it'll still exist.
I`m really interested in this point. One of my three 93 models has 4-1 (stock air box) and it has never felt right in the throttle control area. Harvy once commented (when we had a bit of fun in the twisties with my stock 4-2) that mine seem to pull away quicker coming out of the corners. (nothing to do with gearing - and his is 4-1). So does 4-1 give away some noticeable mid range torque? (Cause it sure feels like it - but more stamina in the straights of course - but thought it could be my imajination as the whole bike has different ergos)
Just got a nice little parcel of goodies from Randy (excellent, convenient, fast, quality service as usual - thanks mate) that includes dual air filter system. So will have my first attempt at changing needle position half a slot using some sort of shim (will search to find out about shim item) next weekend.
(Off topic but- Also got my shiney shiney polished rims with new Roadsmart ll`s ready to fit. Left the wheel centres & spokes acid bathed, standard colour but when we gave the lot an experimental clear powder coat - came up a beautiful heaven gray in the unpolished area - looks great & saves a lot of maintenace polishing - experiment is to see if the clear powdercoat sticks with the shiney perimeter till at least MARCH! --- Heeee he hee :sarcastic: )
Doug,
The shim washers you may need for your change to the Uni filters, you already have. :gamer:
They are just above the E-clip, on the needle, from the factory. Very convenient for 1/2 groove adjustment.
Arnie
Alf,
How do the plugs look?
If they are black-ish you might want to check the fuel level.
DavidR.
Quote from: Arnie on September 16, 2012, 07:03:06 PM
Doug,
The shim washers you may need for your change to the Uni filters, you already have. :gamer:
They are just above the E-clip, on the needle, from the factory. Very convenient for 1/2 groove adjustment.
Arnie
Thanks mate. I will attack it Sunday. :drinks:
Quote from: The General on September 17, 2012, 03:42:17 AM
Quote from: Arnie on September 16, 2012, 07:03:06 PM
Doug,
The shim washers you may need for your change to the Uni filters, you already have. :gamer:
They are just above the E-clip, on the needle, from the factory. Very convenient for 1/2 groove adjustment.
Arnie
Thanks mate. I will attack it Sunday. :drinks:
mate if you can wait I can send up my carb tuning kit, 4lb hammer, 20 inch shifter and a number 3 Phillips head screwdriver :good2:
Quote from: Arnie on September 16, 2012, 07:03:06 PM
Doug,
The shim washers you may need for your change to the Uni filters, you already have. :gamer:
They are just above the E-clip, on the needle, from the factory. Very convenient for 1/2 groove adjustment.
Arnie
Okay, so the shiny washer on top, normally between E clip and little spring, I put under the E clip so lifting needle by the thickness of the washer. I measure the washer at 0.5mm. Then I measure between needle slots and it appears to also be 0.5mm. (or have I got that wrong cause Vernier calipers not that sharp). :scratch_one-s_head:
Therefore wouldn`t the affect mean that I may as well just move the needle up 1 slot? or should I buy a washer or shim 0.25mm? Doug
Quote from: The General on October 12, 2012, 08:35:13 PM
Okay, so the shiny washer on top, normally between E clip and little spring, I put under the E clip so lifting needle by the thickness of the washer. I measure the washer at 0.5mm. Then I measure between needle slots and it appears to also be 0.5mm. (or have I got that wrong cause Vernier calipers not that sharp). :scratch_one-s_head:
Therefore wouldn`t the affect mean that I may as well just move the needle up 1 slot? or should I buy a washer or shim 0.25mm? Doug
It all depends on how tight the plastic piece is on the needle is going to determine if you can use that washer. If the plastic piece is loose then the needle can raise up because the washer is not holding it via the e-clip under the spring.
If the distance of the groove sis the same, lower the clip on notch and leave the washer were it is supposed to be to ensure the needle never slips up causing other issues.
Randy - RPM
Quote from: racerrad8 on October 12, 2012, 08:48:35 PM
Quote from: The General on October 12, 2012, 08:35:13 PM
Okay, so the shiny washer on top, normally between E clip and little spring, I put under the E clip so lifting needle by the thickness of the washer. I measure the washer at 0.5mm. Then I measure between needle slots and it appears to also be 0.5mm. (or have I got that wrong cause Vernier calipers not that sharp). :scratch_one-s_head:
Therefore wouldn`t the affect mean that I may as well just move the needle up 1 slot? or should I buy a washer or shim 0.25mm? Doug
It all depends on how tight the plastic piece is on the needle is going to determine if you can use that washer. If the plastic piece is loose then the needle can raise up because the washer is not holding it via the e-clip under the spring.
If the distance of the groove sis the same, lower the clip on notch and leave the washer were it is supposed to be to ensure the needle never slips up causing other issues.
Randy - RPM
That`s what I figured, thanks Randy. So a full groove height change won`t be too high for the new filters? (ie if it is slightly - it can be tune adjusted for max power/efficiecey)
Given I prefer maximising torque as compared to maximising HP, would you recommend retarding spark generally though ever so slightly from standard? (popcorn)
Quote from: The General on October 12, 2012, 09:25:50 PM
That`s what I figured, thanks Randy. So a full groove height change won`t be too high for the new filters? (ie if it is slightly - it can be tune adjusted for max power/efficiecey)
Given I prefer maximising torque as compared to maximising HP, would you recommend retarding spark generally though ever so slightly from standard? (popcorn)
No, that is the recommended setting I give for the dual pod install when removing the airbox.
You are never going to want to retard the timing. You will benefit from advancing the timing as the torque will come in sooner as the spark is advanced. You will be pleasantly surprised if you advance the timing as the engine is much crisper.
Randy - RPM
The grooves are 1mm apart. (measure from top of one to top of next)
The washers are 0.5mm thick.
So, put the washer UNDER the Eclip to raise 1/2 a groove.
Arnie