I know all engines are different but WTF

SnoDmon · Apr 20, 2014

I've got a 910 par and am having serious fueling problems. Thought maybe you PRO guys could shed some light as theres not many of these in race chassis'. I am having to run stupid lean jets. Like needs to have smaller jets than the 600 did. There was an 800 mono conversion in it last year. Those 2 engines ran single pipes, the 910 has twins. My jetting was:
600 - 360 Mains #2 Needle Position
800 - 420 Mains #1 Needle Position
910 - Started at 490M#5 jumped leaps and bounds down to the 360#1 as thats the smallest in my collection and it was still fat, going to check Dads in the morning.

Now I bought some new Lectron 48's with the 910 and was set up with 6-2XL rods and went to 5-2XL metering rods which were still too rich after tuning them down, also with power jet "shut off". The guy at Packard doesn't want to sell me 4-2XL rods because thats "unheard of" with that large of a carb on that size engine. Between that and Erlandson's advise to take 'em off I decided to "wise up" and take on the Mikuni challenge.

So my question is: does anyone running a 910par CFI need to reduce fuel on their controllers? Or better yet, is anyone running carbs on this engine in a PRO?

Also would like to throw in that with both carb setups, this engine idles really slow. The Mikuni's have had the same size pilot jets for all 3 of my engines, just can't remember the number on 'em. Thanx, and if anyone wants to buy the engine, make me an offer! :devil:

BILTIT · Apr 20, 2014

You have some other problems. My old VES 800 with twins liked 490's, my VES 910 needed more than 490's (1800' elevation).

So you are running a CFI 910 in a pro with carbs?

How are you regulating the fuel pressure down? Fuel injection runs at a much higher pressure and carbs wont work with that pressure.

Everyone that adds cc's needs to add fuel.

snopromod · Apr 20, 2014

BILTIT said:
You have some other problems. My old VES 800 with twins liked 490's, my VES 910 needed more than 490's (1800' elevation).

So you are running a CFI 910 in a pro with carbs?

How are you regulating the fuel pressure down? Fuel injection runs at a much higher pressure and carbs wont work with that pressure.

Everyone that adds cc's needs to add fuel.

What this guy said! You did say race trim, are you running the race sled chassis or the PRO? But if you are running carbs on the PRO, its fuel pump puts out I think 57 psi it's probably blowing fuel right through main jets and straight into cylinders which would give you bad rich condition no matter what size jets you run...

SnoDmon · Apr 20, 2014

No, this is 100% race sled, cfi engine with injector block off plates as the 800 cfi bottom end and a 600 race bottom end are essentially the same. Bolts in with no other mods than injector block offs needed.

What else could cause this? It has always been carbureted so not fuel pump push thru...

Found some 320 mains in Dads collection, next pair jumps to 250 unless I stagger jet.

TRS · Apr 20, 2014

Can you answer these questions. Did you purchase a complete 910 or just the jugs, head and pistons. Do you have the long rod crank installed?

snopromod · Apr 20, 2014

I'm just curious, so did this sled run good before and has just recently started giving you issues or is this a new build and having problems? With information in this thread I still point to the fuel pump if you are not regulating fuel pressure the pump will not kick off unless you eliminated stock fuel pump and installed a diaphragm pickup.. that stock Pro fuel pump is capable of like 80psi, but is regulated like I said to 57psi. So that would make sense you are pushing fuel through every office in that carburetor and creating a super rich condition for motor.

The race sleds are fuel injected now days right? So what are you running for fuel pump/pickup?

PaasoRacing · Apr 20, 2014

The race sleds are still carb... at least up till 2014 they are.

BILTIT · Apr 20, 2014

If it is a factory carb setup then the only thing that could allow that much fuel with that small of jets would be the choke circuit or passing needle/seat, at least that is all i can think of.

mike_s · Apr 20, 2014

If there was excessive pump pressure, it would not force fuel into the engine, it would force it out of the bowl vents. The engine would run rich, yes, but with carbs fuel cannot be "forced" into the engine unless the vents are plugged. In any case, it sounds like the pump isnt one of EFI trim, anyways. Check closely your venting on whichever carbs you're running. I had a case where i installed a new set of carbs and all of the vent line fittings were blocked with locktite, which caused pressure in the float bowls and fuel being forced into the intake tract. Check your float level as well, not sure on the lechtrons, but gennerally the float arm should be slightly lower than level with the float bowl sealing surface (lower as in when the needle is seated and the carb upright). Check and see if the diaphragm in the fuel pump is still in tact. If there is a leak the crankcase can pull fuel through the pump impulse line right past all of the fuel meetering equipment and cause a rich condition. Check your plugs and piston wash, is it just one side running rich? This can indicate fuel bypassing the pump into the crankcase. It was mentioned above, check your fuel enrichment system, choke or primer. Tight cable on choke, or a bad check valve in primer will alow fuel to bypass the meetering equipment as well.

And, finally, if all of this nets no problem found, remember if an engine pulls high vacuum it will require a smaller jet. I had an ultra big bore 800 that ran something like a 340 main my dad had a storm that ran 410 mains and mine was still faster than his...BUT...i still dont see a 900 running something smaller than a 350...Unless the carbs are waaaayyyy too small.

SnoDmon · Apr 20, 2014

Bought complete with long rods installed on my refurbished crank. Case is now from an 800 cfi and has been drilled and milled for pre mix, oil injection check valves have been capped. Brad also said to disconnect exhaust valve solenoids and cap the ports. Sled ran great before the day it blew as an 800. Wore out the crank bearings and digested debris causing piston slap and cylinder/case failure, also destroyed head inserts thus the complete engine.

Factory carb setup installed now. Was never fuel injected. Lectrons seemed to work better on the top end but neither setup has gotten lean enough yet. You guys keep mentioning fuel push through and got to wondering if he barbed the pump pulse fitting in the cfi case correctly and could be getting a faster pulse in the diaphragm?

Chokes are functioning well and instantly dies with just a hint of choke.

I have installed 320 mains and is still rich as well as cold on egts. Will continue to lean out til results are made or problem is found. Trying to throw out theory and read the engine for what it is but can be a difficult task.

I am trying to baseline at a lil over 4,000', lowest parking lot is about 6,000'. Previous jetting was hot to optimal between these elevations. Usually back timing switch 2 degrees when I ride down this low.

Thanx for all the input and sorry for hijacking the Pro-Ride section as theres always over ten times the viewers here. :devil:

SnoDmon · Apr 20, 2014

Botg cylinders running almost exact same egt. Choke and throttle adjustments are perfect Plugs/piston wash are sloppy rich still. Check most recent reply.

Also have an ultra 800bb that I made reference to thinking my richest cylinder was 310 or 320.

Mikuni carbs are 40mm rack style installed now. Lectrons were 48mm.

mike_s · Apr 20, 2014

If the vents on your carbs are not plugged, and fuel is not pouring out of them, the fuel is not pushing through anything. The worst you would have with excessive fuel pressure is fuel in the bellypan and a crummy rich idle.

SnoDmon · Apr 20, 2014

Not clogged as fuel flows freely out while making jet changes. Only fuel in belly pan is from jet change out.

icr · Apr 20, 2014

How much weight are you spinning compared to your 800? It could be the engine is making less hp and needs less fuel. I remember the 910 for the pro was dyno'd by a customer in the 130hp range after struggling with tuning.

SnoDmon · Apr 21, 2014

800 ran 10-58 weights. 600 ran 10-54 weights. I was pulling 8,000 RPM with 10-66 weights on Lectron carbs. I achieved this RPM by pulling fuel away on the power jet until it was "shut off". Started out slobbery and only 6,000 RPM. RPM increased drastically as I turned down power jet and color was found on plugs and pistons but still just a lil bit wet. Wanted to lean out top end a lil bit more but was at the end of adjustment with setup. This could only be achieved at 4,000' and gets worse quick with elevation.

8,000 RPM has not been achieved with Mikuni set up. Brad wanted to see 8,250 out of this engine but I would like to reach 8,500 RPM as that's where ignition is set for on race sleds. When I ran into a lean condition and only 7,500 RPM with the 800, I learned that the ignition is really far advanced at 7,500 and will create a lean spot. I actually dropped from 440 mains to 420's when I reduced weight from 10-62 to 10-58 weights. Seems to me, I'm closer to the dry spot, especially when I gain elevation and RPM starts dropping off so it would make one think that I am farther rich than I will need to be when RPM is spot on.

sledfvr · Apr 21, 2014

My 900 Unionbay ran 350's

geo · Apr 26, 2014

Did you check to see if squish is close during assy?

Have you done the math and used a dial indicator then timing light to confirm your initial ignition timing?

SnoDmon · May 3, 2014

Could measure squish... Brad assembled the engine and I do not believe he checked, think he said something like not being able to change it when I asked. Which we all know can be changed with base gaskets and probably head setup.

Checking the timing was one of the first things I looked at when it wasn't running right initially. I did not get an exact degree of timing but my timing dial box (Race equipment) does change it from one position to another. I would assume about 20 degrees avanced or more in the position I typically run.

We were using a timing light for a car so it was intended for 4 stroke, low rpm tuning. Found an interesting pick up when it would start to run rough, and it woud actually pick up the spark from bottom dead center as both cylinders spark at the same time. To make it even more interesting, when I wired up my Koso gauge (2xEGT, H2o temp, Tach.), I had to run it in what I interperted to be for a 3 cylinder 2 stroke (6 ign. cycles for each RPM signal.)

geo · May 3, 2014

Not familiar with the IQR ignition but a simple verification of TDC and some degree of advance on the flywheel with a dial indicator (before timing light check) might be in order.

IMO if you are building something a custom as you are you need to know the basics are correct before you try to tune.
I thought the original Par motors were a carb set-up like you run. What is their recommendations?

SnoDmon · May 3, 2014

PAR's recomendations is to hang up the phone. Maybe I should have someone else try talking to him. Started with Lectron 48mm carbs he set up with 6-2XL metering rods. Was going to get 4-2XL after the 5-2XL rods were also too rich but went back to the 40mm Mikunis rack carbs instead. Trying 290 mains and finding some snow to test on this weekend. :devil:

I know all engines are different but WTF

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