So I had some time to play again today. I'm between 11.9 and 13 through most all of the power band. Car feels great! Probably the best and strongest yet. The only time I get a bit rich is when I accelerate hard. Just for a moment, when the accelerator pumps kick in. I'm not going to mess with that just yet as I'm not prepared to take the carbs off now. Want to drive baby!
Current setup:
U20
Mikuni Solex 44 PHH
Elevation: 4500 feet
Venturis: 37MM
Pilot Jets: 60 1 1/2 turns
Fuel Jet: 165
Air Jet: 210
B Cam
Going to take it up the canyon tomorrow to see how it does under a good load. Some 12% grades to play with. I really wish I could get a colortune tool on it to fine tune each port. Anyone want to trade the use of a colortune for a power bleeder?
Garm wrote:I'll send you my colortune as long as you send it back, if that's of interest
Really? You would do that? I would pay you for shipping and cost of use. I've loaned out my power bleeder to a couple of members. They have been good at getting it back to me. I would do the same.
Motor is not stock. .20 over with forged pistons clay molded head, ceramic coated piston tops and teflon coated sleeves. Balanced, lightened flywheel, 1 5/8 stainless steel header ceramic coated inside and out.
Gotta love the colour tune.... Gotta love the roadster community...
Ok everything running perfect.... Or is it...
Got it timed and ballanced beautifully... But wondering if the 57.5 idle jets are a little too big ( 155 mains, 180 airs #8 blocks) slight bog down at hard accelleration ie 10 ish
02 sensor ranging between generally high 10 to 15.. With idle around 12.. Sometimes a bit higher sometimes off accelleration a bit lower ie 11.5.... should this be around 13 ?
So do I try the 55 idles again with this setup ?? Will that do the trick... Am I right that lower means less fuel...
Thanks guys ! Greg hope that mail gets there !!!
Cheers
68 Datsun 2000 solex carbs matching number ... Now with long pipes
67.5 number 662
2005 Porsche 997 SOLD
62 karmann ghia restored SOLD
Down under 311 wrote:Gotta love the colour tune.... Gotta love the roadster community...
Ok everything running perfect.... Or is it...
Got it timed and ballanced beautifully... But wondering if the 57.5 idle jets are a little too big ( 155 mains, 180 airs #8 blocks) slight bog down at hard accelleration ie 10 ish
02 sensor ranging between generally high 10 to 15.. With idle around 12.. Sometimes a bit higher sometimes off accelleration a bit lower ie 11.5.... should this be around 13 ?
So do I try the 55 idles again with this setup ?? Will that do the trick... Am I right that lower means less fuel...
Thanks guys ! Greg hope that mail gets there !!!
Cheers
How many turns out are you on the 57.5 pilots? If you are barley 1 to 1 1/2 turns, they may be fine. If you need more than 2 1/2 turns out on the 55's, and it still sneezes, you may want to go back up to the 57.5's.
Down Under, do you have the Solex Carb Manual? I have a PDF I could send if not.
So I've received some interesting info from Lou Mondello in regards to the topic at hand. I didn't know there were two different versions of the type 4/5 carbs.
Here is Lou's email:
" Hey Will, I was reading about the Mikuni jet blocks and preferred set ups etc. One basic fundamental thing is being overlooked. There are 2 types of Mikuni S4 and S5 cars. They are homogenous and independent. The homogenous type uses the "8" jet block and bleed pipes. You cannot put the OA, OB, A or B jet blocks into the homogenous carbs as they simply don't work. The metering of the fuel is wrong. Homogenous carbs are made for a bleed pipe. Same deal if you try and put the 8 jet blocks into the independent type carbs. There are two distinct versions of these carbs and they both have their own assigned jet blocks. One of the mikuni manuals eludes to this in Jinglish. Reading between the lines they specify only the homogenous uses the bleed pipes. Nissan preferred the homogenous on the production cars but independent for racing. I quizzed Todd about the preferred ones for racing but he never answered me. I suspect he does not know there is a major difference. I suspect many Mikuni experts aren't aware of this either. This has caught so many people out so many times and for so long.
Best was to determine what your are is.... Remove 1 idle jet... use a long stiff bit of wire to see if the drilled passage goes directly to the fuel well. If it does you have the independent type. If the idle passage makes a detour to the jet block passage that holds the jet block then you have homogenous. That simple.... You should try this test on 1 idle jet from each carb. I have seen 1 independent and 1 homogenous used on a U20 with the car being woeful to drive. The homogenous ones as supplied by Nissan on the cars work very well up to 37mm choke. After that say with a 40 mm choke and a big cam, the independent carbs work better. I have converted a few carbs from homogenous carbs to independent. The alloy jet block holder has to be swapped over, they are not a listed part in the manual. The fuel trend (delivery) is quite different on both types. I can see why there were 2 type made. The homogenous as supplied by Nissan (69 onwards) on the cars with "8" jet block and "M" bleed pipe were almost fuel injection exactness with a 34mm choke. The early 44 type Q carbs and all the 50's were all independent. Every 40mm mikuni I have seen is homogenous. Hope all this makes sense..... Regards Lou M"
He followed up with this:
"Hey Will, S4's and S5's come in both. If you have a carb off the car, unscrew the 4 long screws that attach the accelerator pump assy to the bottom of the carbs so you can look at the undersides of the main jet area...A pic of this would be good. It will be evident what type they are. All the aftermarket 44 carbs that Mikuni America sold in their kits ,I'm pretty certain were all independent. The ones from Nissan Motorsport USA specifically for the U20's were homogenous. The other types for L series were independent. You can see how people got confused. Also the air correctors are different. You can interchange them but there are very subtle differences in them both. The homogenous carbs should run the "large' type air jet. Big chokes on homogenous carbs do not cause a problem you can actually feel but i was chasing that last 5% to get this mixture trend right on this car. It ran very well on both types of circuits.
Yes very oddball jet blocks you have there. They are independent as they don't use a bleed pipe. I went the the Mikuni shop in Tokyo years ago with my friend Kazuyoshi and the guy there has some stuff that was oddball. I suspect that that that is what you have there. They were probably made to try and fix a part throttle tuning issue. There are a lot of things listed in a Mikuni catalogue that i have never seen.
The OA jet block is exactly the same as the A in every respect. My guess is the Nissan supplied carbs were proprietary so Mikuni had to change the marking for their own aftermarket ones. I have a heap of OB ones here that work well on the early 44 as well as the independent S4 and S5's. Nissan was very closely linked to Mikuni in the early days."
Interesting stuff.
Will
Sorry, I find modern engine swaps revolting. Keep your G, R, or U series in your Roadster!
Down under 311 wrote:Gotta love the colour tune.... Gotta love the roadster community...
Ok everything running perfect.... Or is it...
Got it timed and ballanced beautifully... But wondering if the 57.5 idle jets are a little too big ( 155 mains, 180 airs #8 blocks) slight bog down at hard accelleration ie 10 ish
02 sensor ranging between generally high 10 to 15.. With idle around 12.. Sometimes a bit higher sometimes off accelleration a bit lower ie 11.5.... should this be around 13 ?
So do I try the 55 idles again with this setup ?? Will that do the trick... Am I right that lower means less fuel...
Thanks guys ! Greg hope that mail gets there !!!
Cheers
Well, you shouldn't expect instant throttle response at lower rpms with 37 chokes! Maybe setting the pump rod on the top hole? Yippie! Pull the carb off! But ya, the smaller the number the less fuel, try that too.
Still waitin...
OK, here is a post from Little Cottonwood Canyon. I do apologize in advance for passing on a double yellow. Very untypical of me. I was pulling about a 9% grade at this spot. You can hear the solexes singing!
Sounds great nice clip.
I would hate to be that bike rider, that looks like a heck of a drop off to his right there - with very little road buffer. Not to mention the fact that it's all uphill!
"When all else fails, force prevails!" Ummm, we're gonna need a bigger hammer here.
Will: I already told you about the homogenous vs independent Mikunis - like last year. It's on like the first or second pages of the manual. You have the manual, right?
Skyman wrote:OK, here is a post from Little Cottonwood Canyon. I do apologize in advance for passing on a double yellow. Very untypical of me. I was pulling about a 9% grade at this spot. You can hear the solexes singing!
