Budget engine build

itschrisb

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I’m currently in the process of tearing down and rebuilding my ‘76 xs650. While I have the engine out im debating throwing some money at it to give it a little more pep.

What’s worth doing to these without going nuts? This will be a street ridden bike btw. My budget would probably be around $1000 +/- a few hundred if it’s worth doing more.

Thanks!
 
Prolly your best bang for the buck would be a 750 big bore kit. I have one, though I haven't used it yet. There's several people here on the forum that do have a running 750 kit. Just about every one of 'em say it gives a noticeable increase in power. 500 bucks is a pretty good deal in my opinion.

https://yamahaxs650.com/product/447-big-bore-kit-80mm-750cc/#

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Assuming the engine is fine, good compression etc.... And is coming out of the frame for other reasons. This would be my starting point.

Pull off the top end. Check bores, pistons, valves.

The best possible case would be to hone the bores, fit new piston rings. Lap the valves, refit with new stem seals and springs.

Change out anyway - camchain, camchain guide, tensioner.

Experience from here suggests avoiding the green coloured base gaskets. The one on my bike is slowly extruding itself from the joint.

Goes without saying, rebuild the top end with all new gaskets, O rings, oil seals and brass washers in place of the plastic coated ones fitted to the head studs.
 
Experience from here suggests avoiding the green coloured base gaskets. The one on my bike is slowly extruding itself from the joint.
Yep... the Athena gasket sets. Avoid 'em like the plague, they're junk.
The base gasket on mine has extruded itself over 4mm. It's not leaking yet, but it's just a matter of time. The right cam seal holder did leak. Pulled it and found the green Athena gasket in 3 pieces. Pulled the left, even though it wasn't leaking. It was torn almost in two.

Should be a crime selling junk like that. :poo:

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Maybe it depends .. If the reason for rebuilding is Valves or Cylinders .One budget way forward
can be to take a compression test before and then make an evaluation when it is apart
I don't feel the stock power is weak Provided it is adjusted primarily Carburetors and Ignition.
And one revs it Not so bad I Dont do it so often but it moves
Given the tubular frame and not so strong brakes .. Is there really a need for more
Spirited cornering one needs to pay attention.

But I agree that the price of the kit above probably makes sense Should a re bore be needed
 
FWIW and this is just my opinion. Before you go down a rabbit hole, price out the parts for a standard top-end rebuild and see where you stand. I don’t know what you already have but a top-end and a good electronic ignition is gonna give you all kinds of joy. Then decide how much farther you want to go.
 
Something I never heard very much when this question is asked
Electrics.... If they are top notch that means better power delivery to the coils and points or electronic ignition. Lights and switches. Switches are notorious for power loss

Go through the whole loom, wire from plug to plug or bullet connector. Check condition by continuity checking, remove pins from connectors, check the joins for corrosion or damage. Clean, fix replace connector if it is breaking down. Tedious. but go through every wire. After cleaning go through to the next connection. Do this up to all or any switches, brakes or blinker relay, then continue past, again continuity checking each connection.
When the circuit is done then include the switch or relay by continuity, to see if they are working efficiently..

Remove, dismantle all bar and ignition switchs, clean check solder joins (common for these to have wires loose or strands of the wire detached. Again clean all contacts and lightly grease, ( I use a lithium based white grease), assemble and replace.

All earth connections need to b removed cleaned, some fine sandpaper, making sure the connection to the frame is good then a light contact grease, or I prefer to use nothing then smear a good coating on top.

This alone with a combination of the right coils and plugs will give better fuel economy and that equates to more power. Not much but it all adds up.

For some reason I couldn't copy and past the link. Screen shot of crusinimage 2mm, ( around 190cc) oversized pistons.

Cheap at $80.00+ postage.

Screenshot_2025-03-04-15-07-40-49_cbf47468f7ecfbd8ebcc46bf9cc626da.jpg


Clean up the ports,casting marks, a valve grind, a good electronic ignition coupled with good coils that deliver a long duration and iridium plugs.

Some go for VM carbs, they can b expensive + a bit hungry on fuel. EX500 carbs give good response and those that have them set up properly say they are better than the 650 CV's although they are still a CV carb so will work if changing altitude..

The hardest part is getting the ignition. Bout the only one these days is Boyer and this will eat into the budget.

All this will give a noticeable gain within or around your budget
 
I’m running a 750 kit only and I will say just the reduction in vibes alone was worth the cost. It idles smoother and has some more grunt off the line. Just be realistic. The bike will never be fast, only faster. My vote is for 750 kit, clean up your ports, and get a nice pair of carbs. Most importantly is to get it all playing nicely with proper carb tuning and your electrical running 100%. Otherwise it’s all for nothing. (WOW, I guess grizld really rubbed off on me)
 
Go through the whole loom, wire from plug to plug or bullet connector. Check condition by continuity checking, remove pins from connectors, check the joins for corrosion or damage. Clean, fix replace connector if it is breaking down. Tedious. but go through every wire. After cleaning go through to the next connection. Do this up to all or any switches, brakes or blinker relay, then continue past, again continuity checking each connection.
When the circuit is done then include the switch or relay by continuity, to see if they are working efficiently..

Beer Ok GIF by Busch
 
Yes, do clean up the ports. From the factory, it looks like the lunar landscape in there, lol. full of lumps, bumps, and casting flaws .....

IntakeBefore4.jpg


You really don't want to enlarge them as it's said they're borderline too big already, just smooth them out. All it takes is a Dremel and a few attachments.
 
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