78' cyclone project question

[427cobra]

Well Guys...

Got my Cyclone running today! What I have is a 78' Cyclone that I fitted with the twin carb set up.

I used carbs from Cyclones and jetted to 440 LF specs. I installed ALL new jets.

The engine has been rebuilt new seals/gaskets etc....

The primary has been rebuilt with new "R" weights new silver spring and spacer between the spring and cover plate.
The secondary is rebuilt with a NOS blue spring and placed in the 3 hole with the sportfire cam installed.

Installed a new belt and is running the correct height on the secondary.

I have stock 340 Cyclone gears in the chain case. I used a 80 LF chain case with the roller tensioner.

Has about 125 psi on both cylinders. I did notice the mag side plug is burning a little white.

My problem is that I have a bad BOG!

If I pin the trottle it almost seems like it cuts out then revs up to about 5K. It only goes to about 5-6 grand and thats it.
It starts up nice and idles great. It just has the nasty bog and no top end. I took it up and down the street a few times and it just isnt running right??

So any ideas of things to check let me know!

I think I will go through the carbs again...??? Maybe an air leak? Chokes??

Thanks!

[SpitfireKing]

Haven't dived into my cyclone yet, but can you change the position of the slide needles in the carbs? I know that a lot of guys do that when tuning, and I have done it, but only on 4 stroke Yammi's so far, but sounds like the issue. Does it seem to bog from too much fuel or not enough? If the plug is white sounds like lean issue, so I would drop the needle in the carb down a spot......just a thought...not sure if you even can

[427cobra]

I checked the carb specs and they are correct for the 78' LF. I am running a 35 pilot when the specs call for a 30.

I have th e clip in the 3rd position but it says it should be in the 4th. So I will adjust that tomorrow and run BR10 plugs. I hope this solves my problem...Ill keep you posted

Thanks!

[Matt]

A Cyclone will probably need to be tuned richer then a Liquifire. The benefit of liquid cooling is the ability to keep the engine at a constant controlled temp, which allows for leaner tuning. You may also want to consider that many times in dual carb fan engines, the clutch side is jetted a bit richer, because it runs hotter then the fan side.

[harleysportster]

Good point Matt.

[400brian]

Eric, what size mains are you running?

[flames4555]

Hey guys,

I did a similar concersion on a 76cyclone 440 using a complete liquifire set up including the air box. I'm currently running 180 mains , 40 pilots , clip in the third position, 93 octane fuel mixed @ 40 to 1 and br10 plugs. This set up works pretty well and after a good day of riding the twisty trails around here the plugs are a nice medium brown. I haven't actually done any extended wide open running with this set up, but I would definately go up a couple main jet sizes before attempting.
hope this helps

Kevin

[427cobra]

I m using 220 mains. Maybe I should try the 200's or 180's.
The fan side plug is running white while the PTO is black. This is just from running on the stand. I installed BR9's couldnt find any 10's today.
6HD4 needles which I set to the 5th position (seemed to help the bog)
Should I go with 6HD3 needles?

It only revs to 5K and the high speed coil tested 82 ohms when it should be 76.

Hoping to get this thing dialed in for the HOF ride.

So I need to get it rev over 5K and get a even burn on both plugs.....

[400brian]

At 5k rpm, I don't think you are getting an accurate indication of WOT operation.

I don't know what to make of the one black and one white plug. Is it possible that the choke is feeding fuel to the black side?

[427cobra]

Well new plungers were installed and are seated correctly against the carb.

[JDT]

Take a close look at your carb boots. May be a crack on the lean side.

[Danzig...]

6DH3 and 6DH4 are the same needles? Nevermind, you need the -3 or -4 Meaning the 3 and 4 are just clip settings, these needles effect your mid range.

You dont have enough run time on the engine to check piston wash yet, I would jet up to 40 pilots and stay on the 3rd notch.

What happens when you turn on the choke while its running?

[427cobra]

Well by moving the e clip to the 5th position it took away the bog. when i turn on the choke while running it will kill the engine.

I was under the impression that those were different needles....pats small engine has them listed under different p/n's. There is usually an additional number that indicates the e clip position (6HD3-3)

Carb boots are new. I tried the spray test around the carb boots and intake with no changes.

I am leaning toward a failing CDI. I need a timing light to check for cross firing....

I think I will try swapping carbs too to see if that changes the lean condition.

Thanks for all the tips and advice! Keep em coming....

[427cobra]

Installed the BR10's. Now I seem to have color on both plugs. And tried the timing light and I did not get the +. So I dont think the CDI is cross firing.

I ordered some new jets and am planning on trying 200's.

Still doesnt want to run over 6K. So im wondering if the jets will help that? The plugs do seem a little wet when removed.

So Ill have time this week to mess with it....

I am planning on checking everything listed in the FAQ section tomorrow....Ill see how that goes!

[427cobra]

Well after some more testing I found that the spark is cutting out on both cylinders at 5500 RPMS. The high speed coil tested good on the ohm reader. Its got me stumped...

I found that I need to retard the timing slightly. So I will adjust that and see what happens. But it was not off by much.

Any thoughts?