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Carburetor dilemma? '79 400 LTD

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07 May 2021 01:02 #848132 by YamaKawa
Carburetor dilemma? '79 400 LTD was created by YamaKawa
Just curious. I got a 79 400 LTD and wondering if anyone's tried a single carb set up on these and if anyone that has has ever stuck with it. Basically, I'm thinking about getting the stock carbs deep cleaned, jetting checked / adjusted (having fueling issues at 50+ mph), rebuilt (left bank is starting to deep through the bowl), valves adjusted, screws tuned...aka the full carb package. I've cleaned them by hand every year and it's usually JUST enough to get through the season and needs done at least one, if not twice a year (depends on dust storms), never runs quite perfect but never leaves me stranded either. Just looking to do something about that.

Here's the dilemma though-
Option A: take it to the only shop within 50 miles that works on older bikes, because they have a sonic cleaner and will do EVERYTHING to get it running perfectly for ~$250, BUT said shop is currently backed out 5+ weeks, and that's if I drop it off ASAP - meaning I will miss the bulk majority, if not all, of the riding season just having it sitting in a shop. 

Option B: buy a 2-1 manifold, VM34, pod filter, and some jets, do some tinkering for a couple days to tune it as close as possible as I can, be out roughly $300, but ease of maintenance and future cleaning becomes a breeze by no longer dealing with pesky throttle cables (I got sausage fingers), no longer having to worry about removing the battery  and air box assemblies to get to everything, only one carb to clean, etc. 

Option C: just go a head and wrench a hand cleaning out for one more season and get it in shop by winter so it'll be ready to go by spring (the same shop also does winterization and motorcycle storage for about $100). 

I know going single carb with steal some power and maybe a little fuel economy, but the bike is going on 43 years old on original motor / internals, so I don't mind since I'm not exactly tracking the bike / going to redline constantly. The bike is mostly used for a commuter, and rarely sees above 40mph and when it does, it's normally for 15 minutes or less, so a few HP loss is acceptable. 

Planning on getting a newer, bigger bike (hopefully fuel injected), by next year if I can afford it so I can start road tripping in the next few years.

1985 Yamaha XJ700N Maxim (airhead) - SOLD
1979 Kawasaki KZ400H (LTD), bought with 8416 original miles. - 'Tis my baby
1978 Honda GL1000 - SOLD
1995 Suzuki Katana - SOLD

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07 May 2021 07:01 - 07 May 2021 07:03 #848146 by martin_csr
Replied by martin_csr on topic Carburetor dilemma? '79 400 LTD
Do a topic title search for My custom bobber 440.  see quote below.  The pics are gone, but he said the single atv carburetor gave more power.  From memory I'm pretty sure he oriented the pod filter out towards the side. I haven't reread the topic & I don't recall if he got the motorcycle running perfectly or if more "tweaking" was needed.  that's usually what guys say when dealing w pod filters but they rarely report back. hee.  

Thanks for the good comments! The manifold was made using copper tubing, I believe 1.5" diameter. I took 3 90's and brazed them together. I'll post pic tonight.
The carburetor is a mikuni cv off of a 2004 kfx400 atv. I added larger jets and shimmed the needle. I need to get a bigger pilot jet for the cold mornings. When it's cold, the lower rpm stutters a little. When bike is warm, it runs great from idle to wot and will rev about 1000rpm higher than with factory jetted carbs.
It has digital ignition, so the timing is more or less fixed. I plan on oblonging the holes on the mounting plate to advance the timing to tune further.
Last edit: 07 May 2021 07:03 by martin_csr.

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07 May 2021 21:23 - 07 May 2021 21:23 #848197 by YamaKawa
Replied by YamaKawa on topic Carburetor dilemma? '79 400 LTD

 I don't recall if he got the motorcycle running perfectly or if more "tweaking" was needed.  that's usually what guys say when dealing w pod filters but they rarely report back.  

"The carburetor is a mikuni cv off of a 2004 kfx400 atv."

 
Haha, that is a whole different scenario than what I'm talking about for a conversion. Of course he had issues going single carb + pod filter, he was using a CV carburetor! CVs and pod filters rarely get along without taking weeks on end perfecting the tune. The VM34 is a slide-throttle carburetor, and likely won't suffer from the issues CV carbs have with pods as long as I can get tuned fairly close.

Don't take me wrong, I do applaud the effort, but reading up on a single CV carb mod won't help me if I were to go the slide throttle, non-CV carb route. Whole different animals needing completely different jetting and tuning.

1985 Yamaha XJ700N Maxim (airhead) - SOLD
1979 Kawasaki KZ400H (LTD), bought with 8416 original miles. - 'Tis my baby
1978 Honda GL1000 - SOLD
1995 Suzuki Katana - SOLD
Last edit: 07 May 2021 21:23 by YamaKawa.

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08 May 2021 06:37 - 08 May 2021 06:39 #848204 by martin_csr
Replied by martin_csr on topic Carburetor dilemma? '79 400 LTD
I posted that quote to show what carburetor he used & that a single carburetor won't necessarily reduce the power.  You could go with something different. I didn't read the quote yesterday but it says right there that when the motorcycle is warmed up it runs fine at idle & on up into higher revs.  With the side facing filter he probably installed a duct w a 90 degree bend & this may have effectively eliminated one of the problems of tuning a CV carburetor without a stock airbox.  most guys attach the pod filters directly to the carburetors, but adding a duct or extender sometimes helps to stabilize the air flow.  
Last edit: 08 May 2021 06:39 by martin_csr.

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