Maxim 650 carb rebuild question

Hey friends, got 650 Hitachi carb I'm rebuilding to use on my CB750A (Hondamatic). Everything looks good on the rebuild except for two of the air fuel mixture screws were really tight. I was eventually able to get them out and thought I'd replace them, but the threads on what came in the rebuild kit and the threads on the oem look very different. Can anyone verify why this kit (which is said to fit both the 650 and 750 Hitachi carbs) has a different thread?
I'm worried that the heads on the old oem will not stand up to another round of being "gently forced" out again if they get gummed up (and I was using JIS screwdrivers).
Pics below:

 

Oh, and not sure if it matters but these were on a Canadian bike. I think the only difference between US and CAN version was the jets (CAN version had 43 pilots and 112 mains from the factory vs. 40 pilots and 110 mains on the US version). I can't imagine that the threads would be different but also no idea how a rebuild kit could mess up thread size... am I missing anything??
Thanks for any insight/advice.
Toran

 

the early 650 carbs had a course thread on the mixture screws. yours look like the ultra fine screws.

our supporting vender has the correct screws

there is a thread with photo of the screws side by side

 

The Hitachi HSC32 and HSC33 came in either coarse thread (usually 80 - 81) and fine thread (82 - 84?) but there is some contention that there was a little overlap. xj4ever has both styles, you can find them both in the store catalog.

 

good on you that you spotted this before jamming them in!

 

Thanks for the replies everyone!
Toran

 

can you tell us more about this? Does the spacing of the carbs line up with the Honda? Why did you choose these carbs?
Have others done it?

 

Hey Simmy, the 650 Hitachi carbs line up as long as you use CB750k/f boots (not the A boots) so it requires a set of boots, the carbs with a rejet (going to start with oem #43 pilot jets that came with the Canadian model carbs I bought off ebay and #116 mains and hope it's right... also have oem #112 mains from my Canadian carbs and purchased #42 pilots so I can play with jetting some. Also requires a new XJ throttle cable. I know of a few guys with Hondamatics that have done this. One used these carbs for a drag racing bike that he built with a Hondamatic... apparently there are guys who have built out the Matics for racing (Bracket racing I'm told... I'm not a drag racer though).

The CB750 stock A carbs 26 mm; Stock K/F carbs 28 mm; Stock XJ650 carbs 32 mm. 32 mm carbs are the biggest you can fit into stock K intake tubes.
The CB750A was very much "de-tuned" compared to his K and F brothers. 47(ish)hp compared to 67(ish). Three major reasons according to what I've read: Carbs, Cam, Pistons. You can drop a K/F cam and add a bigger set of carbs (the K/F '69-'78 round top carbs, 28mm or XJ650 Hitachi 32mm) and get a good chunk of that back. Not all of it of course without an upgraded higher compression piston which requires a new top end or a bore and bump up to an 836cc. The cam can be swapped without even needing to remove the engine from the frame as can the carbs obviously which makes it a fairly cost effective way to increase power.

I was hopping for a bit more power as I'm using this new to me Hondamatic as the tug for my sidecar rig. I had it on a CB500t that produced around 34hp and I had to run the RPM's really quite high to get around and the expressway was pretty much out of the question for more than a couple miles. I eventually blew up the motor and instead of spending $1,500 (or more) to redo it all found a running CB750A for $450 and jumped on it. Seemed like a weird bike (no clutch) and everyone likes weird right? Plus they are known to be pretty bullet proof like their brothers (or an XJ for that matter). I bought it and then found it was way underpowered... haha... guess I should have read the fine print first

Hence the work to gain some of that power back (I'd like to take my kids on some overnight trips before they're all grow up and my wife enjoys shorter trips in the rig)... so far I've got about $150 into the carb rebuild (Carbs, rebuild kit, different jets, boots, cables)and am looking at a cam for around $50 and have a mechanic friend who will install and tune it all up for about another $300(ish). Figure I'll have a fun rig, with enough power and a little weirder that will hopefully have cost me around 1k.

Toran

 

Oh, and FYI... the place I got the rebuild kits from (Fleabay) actually wrote me back and said they have the fine thread screws and are sending me 4... honestly pretty surprised by that, but thankful.
Toran

 

That is brilliant. If you had a way to 3D search every intake boot on the planet you could fit any carb to just about any engine.
Sounds like you know your Hondamatics, thanks for the read about them. How does it compare to the CB500T?

I've had an XJ sidecar since 89. Sidecars are great for the family guy.
My recommendation is to restore the XJ carbs then stick them on an XJ in need of them, pull the sidecar with that.
This is the XJ technical talk after all, I'm a paid troll to say that LOL.
Seriously, the XJ shaft drive is indestructible even for sidecar duty.
When I had a completely stock 650 Seca attached to my Velorex I could do 140 kph in 4th gear.
An XJ750 would pull 5th gear I'll bet.
What sidecar do you have?

 

Hey Simmy, sorry for the delay... sidecar has no branding I can find so I'm not sure. I do like the idea of a shaft drive for pulling the tug but the novelty of using a Hondamatic seems like a fun but weird experience... I'll have my left hand free to text and ride... Seriously though have thought about adding a cup holder... could actually enjoy a cup of coffee while riding the Matic.
I'm new to the Hondamatic so still learning a lot... I bought it expecting it to be the same as the CB750K/F bikes but it's actually way underpowered (by about 20hp) so I'm remedying some of that with the XJ650 carbs and eventually a CB750K camshaft. The auto is kinda weird, i haven't driven barely anywhere (winter in MI) and have it apart for the winter but every time I've been on it I keep grabbing for the non-existent clutch.
I'd love to see a pic your hack!

This is what it looked like on the CB500t

When all three of my boys were small enough to get them on the rig at once with me.

 

I like the looks of that chair. My Velorex I think is listed at 80 Kilograms and yours undercuts that for sure.
This is my son and a friend summer of 2018. More here https://xjbikes.com/forums/threads/highly-modded-650-seca.85760/#post-505494

 

That is a sweet hack!