Author Topic: 400/4 Rejetting  (Read 274 times)

Offline barry.greene.944

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400/4 Rejetting
« on: June 27, 2018, 07:35:31 PM »
Looking for some help/advice, I’ve installed air pods on my 1976 400/4 I’ve got 42 slow jets and tried 85 and 90 mains but still won’t run without some choke I have 95 mains as well but haven’t tried these yet. I’ve cleaned the carbs and slow jets, air screw is 2.5 turns out, any advice is welcome


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Offline Arfa

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Re: 400/4 Rejetting
« Reply #1 on: July 07, 2018, 01:29:26 PM »
Not particularly helpful I should say up front but... I've just restored my 400/4 and this included a Yoshi big bore kit, yoshi advise rejetting to suit, but don't suggest how much. I had a look at the this site and the US site, and there was rather more advice on the US one as one would expect with rather more people racing etc. An unscientific review of the advice was that for sea level use an 85 main jet was about right, and all the rest of the carb settings remain as standard. so that's what I've done. I've just given it the first service, bearing in mind I'm up to 7000 rpm steadily, with excursions to 8000, and plugs look to me to be on the slightly rich side, so I'll stick with 85 for present. Otherwise the bike runs really well with clean carburation from tickover upwards.
Main jet really only affects mixture at large throttle openings, so I might suspect that you've got some other thing going on if it won't run at all. Perhaps somebody better versed on here may be able to help?
Arfa.

Offline Johnwebley

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Re: 400/4 Rejetting
« Reply #2 on: July 07, 2018, 03:09:01 PM »
how does it run without the pods ??

  the carbs are designed to run with air intake trumpets ,and pods can sometimes upset the clean airflow
lifelong motorcycle rider,and fan

Offline royhall

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Re: 400/4 Rejetting
« Reply #3 on: July 07, 2018, 04:49:58 PM »
how does it run without the pods ??

  the carbs are designed to run with air intake trumpets ,and pods can sometimes upset the clean airflow
What he said. Put the standard airbox back on and make some pipework to under the seat then paint it red. You won't be sorry as it will run good.
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Offline K2-K6

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Re: 400/4 Rejetting
« Reply #4 on: July 07, 2018, 05:54:43 PM »
Are you confident that all of the idle circuit routes are definitely, positively,  absolutely clear?

It appears that the idle circuits aren't working as they should and by applying choke you increase the vacuum to the main jet and pulling fuel in that way instead of through the idle jets.

Also check to make sure that the vents for the float chambers are all clear as it'll compromise any jetting accuracy if they are essentially going to a vacuum status when the engine tries to draw on them.

The idle air screw should give some response in engine rpm if you adjust them when running, if not it would again suggest you've got to very closely verify those particular circuits are clear. They are finicky and cause no end of difficulty until you are sure these are working as expected.

Offline Greg65

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Re: 400/4 Rejetting
« Reply #5 on: July 11, 2018, 07:32:01 AM »
While sorting a badly jetted Suzuki GS1000 with pods the general opinion was to go 3-4 sizes up depending on the quality of the pods.

I then used this guide to fine tune.

http://www.factorypro.com/tech_tuning_procedures/tuning_carbtune,CV,high_rpm_engines.html

Enjoy,
Greg
Keep smiling it makes the management nervous.
Honda CB400 1976
Suzuki GS1000 1978