Author Topic: 350f cutting out, need some input (Read 1544 times)

innovativems · « **on:** June 09, 2019, 03:16:11 PM »

So i'm banging my head on a 350f i've rebuilt. backstory. had someone go through the head and they didn't do a good job and was getting white smoke after firing it up. JMR went through the head and the bike has next size up pistons and rings and was machined to hondaman's recommended clearances. Pistons are right side up and gaps are in spec.

Been working to break in the top end and it's fighting me. Bike will fire right up, and after about 60 seconds will get to a point where it really struggles to go from 4500-6500. Feels like a mis-fire but it will get past it and then pull fine. Carbs were cleaned and rebuild with stock size jets from K&L, float height is set to stock. I have swapped coils with another set i had, new plugs, and even swapped out the dyna ignition for a set of points. None of these changed the behavior. It's running on my motion pro aux tank. plugs are black and sooty when i pull them. but the way it struggles i'm not surprised. Screws are at 7/8 turns out and carbs have been vacuumed synced. It's stock airbox and filters with delkevic 4 into 1 with the baffle installed. Removing the filter and lid made no difference, using choke at all made no difference.

I havn't tried moving the needles and i havn't removed the vent hoses from the carbs.

Any thoughts from anyone would be greatly appreciated.

Jarrett_Honda · « **Reply #1 on:** June 09, 2019, 03:54:59 PM »

Sounds like it's too rich. If a bike is too rich it won't have power when accelerating or going up in RPMs. You even said that the plugs were black and sooty.

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innovativems · « **Reply #2 on:** June 09, 2019, 05:27:16 PM »

That’s where my heads was at. Seems to be in the needle range of throttle. Too.

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Robbo · « **Reply #3 on:** June 09, 2019, 05:28:26 PM »

First thing to try is turning the air screws out. This will lean out the air/fuel mixture.

I would go in 1/8 increments up to 1 1/4 turns.

If there is no improvement, then move on to needle position.

If still no improvement, move to changing jets. If you get this far, make sure to reset air screws to 7/8 and needle position to stock. Then repeat the steps starting with small adjustments with air screws if necessary.

Also, make sure to write down the settings and make notes on how the bike behaves.

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innovativems · « **Reply #4 on:** June 09, 2019, 05:49:14 PM »

It’s been no change with adjusting the screws. I’ll do needles next.

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Robbo · « **Reply #5 on:** June 09, 2019, 06:01:20 PM »

Have you done a plug chop when riding at a constant speed in the 4500-6500 rpm range? Say around 5500rpm?

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Robbo · « **Reply #6 on:** June 09, 2019, 06:03:33 PM »

Can you list all the jet sizes and needle and if they are stock or aftermarket components in your current setup?

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Jarrett_Honda · « **Reply #7 on:** June 09, 2019, 06:03:52 PM »

Sounds like most of everything is stock. If that's the case then you shouldn't have to use different jets.

How many turns ate you set at now? You're going to have to check plugs as each cylinder could be different.

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innovativems · « **Reply #8 on:** June 09, 2019, 06:04:47 PM »

It’s cutting in and out so bad at that range I can’t keep it there for too long

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Jarrett_Honda · « **Reply #9 on:** June 09, 2019, 06:06:23 PM »

Can you show use a picture of your plugs?

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innovativems · « **Reply #10 on:** June 09, 2019, 06:11:21 PM »

Quote from: Jarrett_Honda on June 09, 2019, 06:06:23 PM

Can you show use a picture of your plugs?

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All four look identical

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Jarrett_Honda · « **Reply #11 on:** June 09, 2019, 06:13:38 PM »

Quote from: innovativems on June 09, 2019, 06:11:21 PM

Quote from: Jarrett_Honda on June 09, 2019, 06:06:23 PM
Can you show use a picture of your plugs?

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All four look identical

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Holy #$%*! That's darker than me. How many turns out is this?

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innovativems · « **Reply #12 on:** June 09, 2019, 06:17:53 PM »

7/8-1.5 no difference. The real problem is right at 1/2-3/4 throttle. The needles are stock and I used the emulsion tubes that were in the k and k kit. Now that I think about, that could be causing an issue

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Jarrett_Honda · « **Reply #13 on:** June 09, 2019, 06:29:02 PM »

Your choke isn't on by mistake is it?

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Robbo · « **Reply #14 on:** June 09, 2019, 06:30:52 PM »

Quote from: innovativems on June 09, 2019, 06:11:21 PM

Quote from: Jarrett_Honda on June 09, 2019, 06:06:23 PM
Can you show use a picture of your plugs?

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All four look identical

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What RPM was the bike running at?

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innovativems · « **Reply #15 on:** June 09, 2019, 06:31:49 PM »

Quote from: Jarrett_Honda on June 09, 2019, 06:29:02 PM

Your choke isn't on by mistake is it?

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No sir

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innovativems · « **Reply #16 on:** June 09, 2019, 06:32:10 PM »

Quote from: Robbo on June 09, 2019, 06:30:52 PM

Quote from: innovativems on June 09, 2019, 06:11:21 PM
Quote from: Jarrett_Honda on June 09, 2019, 06:06:23 PM
Can you show use a picture of your plugs?

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All four look identical

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What RPM was the bike running at?

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Right about 4500-7000

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Robbo · « **Reply #17 on:** June 09, 2019, 07:10:56 PM »

What sort of numbers did you get on the carb vacuum synch?

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innovativems · « **Reply #18 on:** June 09, 2019, 07:32:13 PM »

Quote from: Robbo on June 09, 2019, 07:10:56 PM

What sort of numbers did you get on the carb vacuum synch?

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Nothing out of the ordinary. It’s the motion pro set that uses fluid to sync them

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robvangulik · « **Reply #19 on:** June 10, 2019, 12:37:34 AM »

There is nothing under the saddle blocking the air intake? Air filter is clean?

innovativems · « **Reply #20 on:** June 10, 2019, 04:52:00 AM »

Quote from: robvangulik on June 10, 2019, 12:37:34 AM

There is nothing under the saddle blocking the air intake? Air filter is clean?

Brand new filter. It’s open under the seat. I’m going to try running it without the lid and then air filter to see if that makes any difference to make sure to verify it’s rich in the mid range.

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Bodi · « **Reply #21 on:** June 10, 2019, 07:20:02 AM »

"stock size jets from K&L"
Red flag.
Try OEM genuine Keihin lets and emulsion tubes. Why did you replace them? These parts are very durable: they do wear (particularly the emulsion tube, needle, and main jet - from needle contact) but that's after many thousands of miles.
Weird mixture issues are very common with aftermarket carb kits.

innovativems · « **Reply #22 on:** June 10, 2019, 06:43:22 PM »

Quote from: Bodi on June 10, 2019, 07:20:02 AM

"stock size jets from K&L"
Red flag.
Try OEM genuine Keihin lets and emulsion tubes. Why did you replace them? These parts are very durable: they do wear (particularly the emulsion tube, needle, and main jet - from needle contact) but that's after many thousands of miles.
Weird mixture issues are very common with aftermarket carb kits.

Thanks for that information. Pulled the air box lid and filter and confirmed it’s just rich as all get out. I’ll hunt for the stock brass

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Author Topic: 350f cutting out, need some input (Read 1544 times)