MicroSquirt.com read only forum (Jan.15,2018)

At the risk of enhancing your challenges by raising this point again, I'm struggling to understand the fuel requirements you are advising on
So, 2 cycle, 440cc twin and your finding 85lb injectors to come up as calculated "not enough".
Just to compare to my 4 cycle "lump" as some have referred to it as, I'm currently running two 30lb injectors on a 980cc twin, and realizing about a 100hp output with modest boost, and reasonable efficiency. I had been using twin 45lb Delphis, but found issues keeping required fuel above the minimum recomended 2.0 . I can't fathom needing full delivery on twin 85lb injectors at 3 bar, following standard fuel consumption to horse power ratings. However, if that is the 2 cycle difference then I stand corrected. The fuel has to go somewhere, so if your exhaust isn't all slobery and plugs are looking dry then yes you need more. On the other hand, are you certain your fuel pump isn't running out of flow? Also, what do other sleds require - what is normal on other injected product?
Hope you solve it, Lorne.

I've done some research on other fuel injected sleds and have not been able to come up with concrete numbers for injector sizing. I was orginally looking for OEM snowmobile throttle bodies w/injectors for my project; but was unable to find vital info pertaining to my specific requirements.

I am using a fuel pump out of another snowmobile producing 160+ hp from a 1000 cc twin 2 stroke. I first looked into the fuel pump being the culprit and have found no evidence to support this.

Looking over and over the microsquirt information I have begun to believe that my problem lies in the time to inject the required fuel @ 8000+ rpm and not hp produced by the engine. I could be wrong, and I will be the first to post on this forum that I was.....but from the tuning I've done and the symptoms I have experienced I believe that I can not get enough fuel to the engine.

FYI my 55 hp carb'd sled gets 8 mpg on a typical trail ride. (This is with leaner jetting than stock settings.)

Well one thing that would help remove certain variables off the table would be to plumb a fuel pressure gague to confirm what the injectors definately receive during those runs where duty cycles are going so high, yet lean readings are encountered. I've had such a development where I had no idea my return line had plugged and caused the opposite with really high pressure and fuel delivery behaviour, without the gauge I could confirm either way

I will start looking into pressuge gauges, definitely a useful tuning aid. What kind of a setup did you end up using?

My set up has gone through many changes. Currently, and being a motorbike (and not wishing to modify stock parts) I have a special fitting on each flank of the lower tank suction ports that allows "suction/ return" and an internal standpipe to avoid recirculation. The fuel pump is mounted externally (Bosch) and supplies fuel to 4 injectors. Two are right down adjacent to the inlet ports (traditional) and two are about 14" removed back up by the twin bore throttle body plates (spraying @ 90 degrees to plates to enhance vaporization). There are different pro's and con's to each location, but I have a switch on my left handgrip to switch between locations (another long story). I can enjoy enhanced fuel economy when cruising on top ports, or switch back to lower ports to gain stability under varrying throttle conditions (in town). Wall Wetting becomes a factor for the removed location, etc. etc. and I found "Extau" a slippery slope to negotiate.
I have a manifold referenced pressure regulator that allows return flow back to tank (probably best method to keep heat in check on close quarters bike, other than the returnless PWM control systems which I haven't really tried yet).
I had a return line plug up a couple of years ago and was shocked to measure 100psi at my injectors - had been on a reasonably long trip but was back in garage when the coin dropped. AFR swings on that trip were rather gross. I have since left a spare test port (1/8npt is small enough to hide) to check pressures at any time.
Listening to your U tube movie taken running your sled - the engine sounds like it is starving? What sort of fuel system have you rigged, and is it a complete change from original set up (sled was carb prior to MS?)
Good luck on tests,
Lorne.

Sled was a carb'd racing sled. Started out running 110 octane w/premix.

I did a total rebuild, including drilling oil passages to convert it to oil injection. Ran it on the carbs for the first 10hrs for proper break-in, and to ensure the oil injection was working as expected. On the sled is a timing box with 7 settings. Timing was retarded and compression reduced to accommodate 92 oct. (Running 94 because it's non ethanol in my area.)

Current fuel setup from tank back to tank:
-External fuel pump from a skidoo 1000 twin 2-stroke. It pumps a HEALTHY amount.
-fuel filter
-2 throttle bodies w/ 2 injectors, custom fuel rail w/ 2.5 bar regulator (I have a 3bar also).
-separate return line to the tank.

also running heated WB O2(might be removed due to Wattage produced by stator), MAP, CLT, IAT, A Hall sensor is used for the the tach signal.

What sort of wattage on your stator? Fuel pumps draw lots, perhaps voltage drop off is a fueling factor?
(that's another aspect of my project - the stock BMW Bosch alternators were reknowned for low output and I removed and upgraded from a potential of 280W at speed, to 900W just above idle to ensure there would be no lack of electricity for any occasion).

Stator is rated for 280W. I have put the sled on an electrical diet, and my battery voltage now seems to steady. If I ditch the LC-1 controller and go to an HID headlight kit, I should still be power neutral using LOW-Z injectors. This is probably one of the advantages of my motor rev'ing so high (shown in the video), the stator output should be very close to the rated 280W while riding.

How can I measure the Fuel pump draw while the motor is under load? i.e. riding.

That's kind of like asking how I tune my bike while I'm riding it
Of course you're not supposed to entertain that type of distraction (I use very quiet back country roads not frequented by black and whites, have the lap top securely mounted to a bracket atop my fuel tank, and try to pull over to make significant alterations in TS).
I would suspect however that you might just strap on a meter to your sled, with a current measuring range of at least 10amp (I know my Fluke will handle that), and just have it placed such that you might glance to the screen at that time you are running. I think however that the current consumption may actually drop off as the fuel flow increases (where less is being pushed back to tank via the pressure regulator) and in that case just sitting stationary running the engine might provide the best indication of max amps used by the pump (just my guess at this point).
Good luck,
Lorne.

I will definitely look into that. I can't wait to get this thing screaming.........

http://www.youtube.com/watch?v=Umn8tigP ... e=youtu.be