R1 Carbs (lots of pics)

[datzenmike]

Take it off and port match it to the head and/or the head to it. This should have been done already.

 

- When driving around in freezing temps and conditions are damp, the engine can miss under load and lean spikes. I suspect freezing is temporarily blocking the main jet. Apparently Silkolene ProFST is a good fuel antifreeze which I might try. I might also tap into the cabin heater's coolant line and run it through the carb.

 

 

 

 

Doubt this will work for carb icing, though they may tell you this. Most Canadian gas is 10% ethanol to begin with. Take a look at the contents... ethanol is the main gas line anti-freeze ingredient. What happens is the already cold damp air is further cooled by fuel evaporation, well below the freezing point. Carb parts in the path of the damp air are so cold that frost forms on them. Gas line anti-freeze is just that... gas line. Only easy cure for carb icing it to run warm air. All stock carb engines have an ATC (Auto temp control) set ups on the air filter housings. t just pipes warmed air from the exhaust manifold to the carb. Simple and effective it regulates the intake air to about 100F. Car runs at 30 below like it's July.

 

 

[G-Duax]

Just about finished with my bike carb set up.

Carbs are from the 1980 Vance & Hines Pro-Stock drag bike, 40mm smooth bore Mikuni VM series.

Mikuni short L4 manifold, with a 240Z filter assembly. The opening at the front of the filter housing was enlarged so 4" accordion hose snaps in.

 

Still to do: run all the vent lines so that if a float sticks, the carbs won't pee raw gas onto the exhaust manifold.

Replace ratty 4-1 throttle cable, and adapt end to the 620 firewal attachement point, and gas pedal.

 

 

 

 

[datzenmike]

Could the overflow be plumbed into the return line?

[G-Duax]

Nope, because with the 280Z fuel pump I have, pressure in the return line is at 2 psi, even with a lighter relief spring in the pump.

 

Got to get to some hardware stores, and see if I can find some 3/16" barbed T fittings, to tie all 4 bowl overflows to one line, and then maybe go forward to a cooler point in the bay to let any spillage drain.

 

And I don't look forward to figuring out the jetting.

Whats the chance that carbs jetted for a 14,000 rpm 1000cc bike engine will be any where close to a 1900cc (I mean 1600cc ;) ) Datsun ?

My thoughs are slim to none...

[datzenmike]

There shouldn't be any pressure in the return line, it's open into the tank. Fuel just rolls down hill into it. There is a small restriction on the engine side of the return. This is so pressure will build on the carb and pump side. If it was open the gas would all just fall back into the tank.

 

 

Did I mention how sexy these are?

 

 

 

 

 

 

[G-Duax]

Shouldn't be any restriction, but......

Have a fuel pump from hell, and the return line was so clogged when I bought the truck, that I had to auger it out with ever increasing lengths of 1/8" stranded steel cable, so I'm pretty sure it isn't full diameter all the way back.

 

I'll try to remember the 'sexy' thing as I try to figure out the jetting.......

Simple job on a single cylinder dirt bike, but I think it will be a pain in the a$$ leaning over a fender.

 

A buddy of mine just asked if an old truck engine can create enough flow to make these work.

I said 'sure, after it exceeds the factory rev limit'.

[datzenmike]

 

Here's the restriction on the L20B engines. Without it, gas from the pump would take the easy path back to the tank rather than having to force the needle valve open. Imagine a garden hose with a small hole in it. Not much comes out the 'leak' because the other end is open. Now place your finger over the big end and try to squeeze off the water flow. Your finger is the restriction that builds pressure... and now the small hole is spraying across the lawn.

[scooter]

Those are some nice carbs, I really like that setup. Post your results if they are jettable and streetable

[G-Duax]

 

Here's the restriction on the L20B engines. Without it, gas from the pump would take the easy path back to the tank rather than having to force the needle valve open. Imagine a garden hose with a small hole in it. Not much comes out the 'leak' because the other end is open. Now place your finger over the big end and try to squeeze off the water flow. Your finger is the restriction that builds pressure... and now the small hole is spraying across the lawn.

 

Although not exactly what I have Mike, I do run something simular on the Weber DGV that I am running.

I used 2 inlets hose barbs on the carb, with one being fed by the fuel pump, and the other was brazed shut, and the bleed hole drilled (just like your picture), and that went to the return line.

 

All was fine & dandy when I had a Holley 'Red' pump feeding everything, but it failed.

So the Z-car FI pump was mounted, and it was way too much, even with the weak spring installed in the Z-car's built in relief valve.

So the brazed bleed hole was drilled out completely. A gauge was installed just past the carb, and getting I'm getting 2 psi just past the carb.

 

I know I have to play with the pump some more, to reduce it's flow. Maybe a resistor, to cut the voltage down, thus the flow rate.

Maybe change out that great pump, for something a little less efficiant.

[Tom1200]

On my FCR flat slide carbs I use a cheap arse facet fuel pump with a cheap arse Holley regulator set to just under 2 psi. No issues at all.

 

As for the jetting slam dunk: make sure you have a jet wrench if you don't already. Start with the main down, then go to the pilot etc. the needles are likely to give you the most problems as the may be specific to the drag bike.

 

I was in the same predicament with my flat slides; they came off an A13 powered 10,000 rpm sports racer that made near double what my car did. The car was horribly rich; even with no load (neutral) full throttle would practically kill the motor. I went down 4 jet sizes at a time until it would motor carburate. The pilot jets were a bit tricky as the cam in the motor had a ton of overlap, so I actually had to go leaner. I was revving the motor and notice it belched fuel out of the velocity stacks. The other issue was around 5500 RPMs 5/8ths throttle; rolling on the throttle to quickly got an ever so slight bog. I poured though the Keihin jetting charts and determined shorter needles with more aggressive taper would fit the bill. The clip was on the bottom postitiin (full rich) and it still went a bit lean. All this was with my A12 motor that made a shade over 80whp at 8300 RPMs

 

The A15 has a Delta 278 cam (fairly mild) and I had to go richer on the pilot jets and the mains, it's making around 105-110whp. The car now hits 111mph before turn 4 at Spring Mountain Motorsports.

 

 

Tom

[G-Duax]

That's one wicked A-series Tom !

 

And yes, I have a couple of main jet tools that I bought back in 1975. Unfortunately, I don't have the large collection of jets & needles from back then.

Already found an eBay seller who had a large pile of main jets, and I have soldered them up, and re-drilled them in years gone by.

Needles & pilots will have to be aquired though.

[Tom1200]

I can't remember which is which when it comes Keihin and Mikuni carbs but one brand the jet number is the actual measurement where the other is a number. I'd have no issue with soldering jets up as long as you have an accurate way to drill out the solder. My carbs came with a slew of jets but I still bought about $100 worth, mainly because of running an A12 and A15.

[G-Duax]

Someone used to make an adjustable main jet assemly for these old Mikuni VMs back in the '70s, but so far only one has surfaced on eBay, and I've not found any stashed on a dealer's shelf yet..

It replaced the bowl plug, and worked pretty slick.

 

They were like this:

http://www.aim-store.de/de/Sonstiges/Hauptduese/Verstellbare-Hauptduese.html#

 

And this is helpful:

 

[MantisX620]

Im going to tap the 4 runners of my bogg bros manifold and run them to a vacuum block. Then I am going to run the block vent to a catch can and the catch can vent to the vacuum block. I also want to hook my booster back up to the vacuum block. Anyone see any issues with this plan?

[G-Duax]

Pleanty......

Leave the crankcase vent & catch tank by it's self.

You will lose too much braking power if you hook it up to the vacuum system.

 

Don't forget a check valve between the brake booster & vacuum source.

 

If you are tapping the runners 1/8 NPT, I have some small in-line check valves that screw into the runners, that will yeild better vacuum, since not all bores are pulling at the same time, and connecting them to a manifold will allow some of the vacuum signal to pass over to cylinders that are not drawing.

[datzenmike]

In advance I apologize, but there are over 60 pages of info here. Assuming the R1 carbs run well of themselves I need....

 

Vacuum advance for the distributor. I found mention of it but no follow up. Is there a vacuum port for this? or just intake vacuum? Can someone give me the page that answers this? 

[MantisX620]

My manifold came with a port on the #1 runner but It seemed to suck all the time so I have it unhooked.

[datzenmike]

Distributor is designed to work on ported vacuum. No vacuum advance at idle and slowly increasing vacuum as throttle plate rises above the port and intake vacuum applied to it. (less than 1/8")

 

SU's have a vacuum advance port. How does that work?

[MantisX620]

So I was looking up something, and came across these.

 

 

Does anyone know if these might work if something similar was made to place directly behind the carb outlet? Seems like a neat way to get a genuine vacuum signal.

 

MantisX

[wayno]

Where did you find these?

They likely will not work for the vacuum advance as the hole is to far away from the butterfly valve, all the holes I have seen controlling the vacuum advance are within an sixteenth inch of the butterfly valve, and are a ways away from the shaft, but it might work if put on to where the hole was near the shaft, but I think too far away.

So I was looking up something, and came across these.

 

 

Does anyone know if these might work if something similar was made to place directly behind the carb outlet? Seems like a neat way to get a genuine vacuum signal.

 

MantisX

[Lockleaf]

They will work, they will just be manifold vacuum, not ported. It may not be perfectly optimal, but it is totally functional.

[DADZSUN]

Take it off and port match it to the head and/or the head to it. This should have been done already.

 

 

Doubt this will work for carb icing, though they may tell you this. Most Canadian gas is 10% ethanol to begin with. Take a look at the contents... ethanol is the main gas line anti-freeze ingredient. What happens is the already cold damp air is further cooled by fuel evaporation, well below the freezing point. Carb parts in the path of the damp air are so cold that frost forms on them. Gas line anti-freeze is just that... gas line. Only easy cure for carb icing it to run warm air. All stock carb engines have an ATC (Auto temp control) set ups on the air filter housings. t just pipes warmed air from the exhaust manifold to the carb. Simple and effective it regulates the intake air to about 100F. Car runs at 30 below like it's July.

 

 

 

I plan to match the intake to the head this winter.

 

W/R to the gas, I actually try to run non-ethanol to better maintain the carb's rubber seals. Silkolene Pro FST is marketed as a remededy for carb icing and the reviews online are quite favorable. It certaintly doesn't hurt to try.

 

There is another solution albeit it takes a little longer to take effect. The R1 does have a provision to run engine coolant through the body. I'm thinking of using a couple of 'T' junctions and plumbing it into the cabin return line (so the coolant is only 'heating' the carb when it's cold enough to activate the cabin heater).

 

Coolant In

 

Coolant Out

[G-Duax]

 I'm thinking of using a couple of 'T' junctions and plumbing it into the cabin return line (so the coolant is only 'heating' the carb when it's cold enough to activate the cabin heater).

 

 

Nice idea....

[datzenmike]

Carb icing cannot be cured by an additive. No matter what they say. Fuel evaporation absorbs heat. Wet your hand with gas and blow on it. The lower part of the carb in fact much of the carb becomes much colder than the air around it, even if it's in the 30s. Moisture in the air freezes onto these cooler parts. I've had the venturi covered in frost and the car stops running. The cure is the ATC automatic temperature control. This mixes cold air with warmed air drawn from the hot exhaust.

 

Anything added to the gas can prevent fuel lines from freezing. To have a fuel line freeze two things are needed. It must be below freezing and there has to be water in the fuel line. This was true before ethanol was added and gas was only gasoline. Gas line anti freeze is just methyl hydrate. Water does not mix with gas but It mixes with alcohol and it, will mix with gas. In this state it will stay liquid at freezing temps and flow through the carb and be removed.

[DADZSUN]

To have a fuel line freeze two things are needed. It must be below freezing and there has to be water in the fuel line.

 

I'm not worried about the fuel within the line freezing. It's when cold (< 0C) and damp air is exposed to the carb that the intake air itself crystalizes and temporarily locks up the carb's mechanical bits from functioning normally. I'm assuming this additive helps prevent the intake charge and/or the mechanical bits (slider/needles) from freezing.

 

A quick Google explains it as this: " Carburetor icing occurs when there is humid air, and the temperature drop in the venturi causes the water vapor to freeze. ... Icing may also cause jamming of the mechanical parts of thecarburetor, such as the throttle, typically a butterfly valve."

 

I don't drive my 510 when the road salt comes out so I've only experienced it once, and it was about -3C and the weather was almost foggy despite being below 0. The car had a noticeable, random (ie: 2-3 times/min), and fairly strong stumble that I've only experienced that one time. It was strong enough that I was discouraged from driving it any more until I figured out the cause. A couple of days later with ~ +8C she ran perfectly fine.