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#1 Idaho Hillbilly

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Posted 15 December 2017 - 09:13 PM

Hey all, been on and off the forums for years. I've now acquired a total of 3 620's and finally have one that I'm actually planning to build. Picked it up several months back and parked it in the corner of the shop. Ordered my first batch of parts for it last week and just finally decided to see if I could make her go. Supposedly was in storage for at least 10 years before I picked it up (out of the storage unit). Has a Detroit locker in the rear, a completely rust free body (literally have not found ANY), L20b with a cam (supposedly) and Mikuni 44's.

 

First batch of parts was a little random, but I picked up front and rear window seals, full engine gasket set, spark plugs, timing set, brake master cylinder, clutch master cylinder and slave cylinder. 

 

I was told that it had a blown head gasket when I bought it, but thought the first thing i'd do is see if I could get it fired up and test that out for myself. Did a quick swap of the fluids, ran a dedicated fuel line to a gas can with new fuel, threw the new plugs in it and started cranking. To my surprise, it took off pretty quick, but idled quite rough. Give it some throttle and it smooths out and actually revs quite well. Started pulling plugs one at a time to determine the cylinders that were not firing. I found that I could removed both plug wires for cylinders 1 & 2 and have no change in engine operation... bummer, blown gasket between one and two?! Removed plugs and performed compression test on both cylinders... 175psi in #1 and about 160 in #2... huh, well maybe they have the firing order off? verified that it was correct at 1324. Verified that the front carb is fueling (it is). 

 

This is where I currently sit. I am kind of thinking that the front carb is actually over fueling to the point that I have a dead miss on those cylinders? On that topic, I'm sure that these carbs could use a solid rebuild. I don't know anything about them... what is the best option for having them rebuilt? 

​Pics below of what I'm working with! Looking forward to the build with you guys  :)

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#2 Str8jacket

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Posted 15 December 2017 - 11:20 PM

Multiple carbs are super finicky in regards to being sync'd at idle. As in they all need to be identical in their throttle position or they will idle like crab, higher up in revs they tend to be less intolerant. Make sure the linkage is adjusted correctly, try removing the centre link between the carbs so they are independent of the other pair of cyls. See if idle improves. If so more work is needed on your linkage adjustments.

Set both carbs to the same idle screw setting. A carb sync tool makes checking easier. Google 'best lean idle' it will help,i saw a sticky in the engine section for setting webers it is the same over all process for mikunis.

Check the entire ignition system, check your initial advance i ran mine somewhere around 14 degrees for mikunis from memory.
Eventually once running you will need to establish the advance curve, about 32 degrees worked for mine all in around 3000rpm. Vac advance may or may not work depending on a bunch of things.

Ignition is half the issues with ir carbs, throttle linkages is the other half. Get them right first.

Fuel pressure needs to ne about 4psi max.

Hope that helps a bit.

#3 Str8jacket

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Posted 15 December 2017 - 11:25 PM

Oh yeah depending on linkage set up you can twist the throttle shaft and have one throttle plate slightly open more than the other on the same carb. I ran stops adjusted so that both plates are supported and no twist can occur between throttle bores.

Get rid of any vacuum leaks too. That will ruin your week.

#4 wayno

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Posted 15 December 2017 - 11:44 PM

The firing order is 1, 3, 4, 2, counter clockwise, I repeat COUNTER CLOCKWISE, it is not 1, 3, 2, 4 like you said above in the first post.


 

 


#5 Idaho Hillbilly

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Posted 16 December 2017 - 08:50 AM

Thanks guys. I'll double check the timing to make sure I had them in the proper order. Pretty sure I just typo'd above, but I'll take a look. It also appears that I need to host the photos somewhere else...

I've never seen a cylinder over fuel so bad that it would not fire at all, but I can unplug 1&2 independently or at the same time and have zero change to the engine.

#6 wayno

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Posted 16 December 2017 - 09:23 AM

Yea, try Postimage, Photolame ruined millions of photos on forums and the like all over the world, one would hope that place was history, but they are still around to screw with normal people.

I am surprised it will even run on 2 cylinders at all, the engine would likely be running really rough.

Maybe it is getting too much fuel in #1 and #2 and flooding out.


 

 


#7 Stoffregen Motorsports

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Posted 17 December 2017 - 09:09 AM

I don't know what you paid for the truck, but those carbs are worth a few bucks.

 

Good luck with your build.

 

Note - If you can't get the other carb to work, it may be plugged up. There's a spot in the accelerator pump cavity that gets calcified.



#8 Idaho Hillbilly

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Posted 27 December 2017 - 06:27 PM

Haven't been able to get back to the truck yet. Big snow storms, Christmas and too busy in the shop. I'll toy with it more after the new year hopefully so I can give some updates. Hoping to see how it runs with these carbs on it. Not really sure I like the filterless system where I live. I'll have to figure something out there or swap it all out for another setup. 

​Picked the whole truck up for $1200, figured the carbs were worth 2/3 of that anyways. The locker is pretty cool too, and where I live, a rust free body is priceless. 

​In the meantime, here's Ol' Red hiding behind a snow berm.

 

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#9 banzai510(hainz)

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Posted 28 December 2017 - 10:44 AM

if a fuel jet block backs out from the Mukunis it will flood out.

 

I notice onmy 44s I need to choke more to get started.  (NO pumping of gas)  I don't see a choke cable

 

On my Mikunis 40s I just pump the gas a few times and it starts


Throw on some Weber sidedrafts, Rising Sun hood.... call it good

#10 bananahamuck

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Posted 02 January 2018 - 03:41 PM

 Northern Idaho is gods country man ..

 

:thumbup:

 

/


So somehow while i was driving back from Eaglerock swap meet i somehow caused YOU to post this,,,, do really think members on this site are that stupid to believe i caused it??

http://community.rat...un-for-a-while/

Yeah i guess you do,,

 

BTW ,,,, the first person to call you a pussy,,,, ya might wanna check out his ethnicity ,, cuz i don't think it's what you think it is there snowflakeboy

 


..........................I shall call it, narclops.