First post! Working on a '79 Special engine

[Nercitar]

Hi everyone,

I am currently doing a build of a 1979 XS650 Special, going to make it into more of a standard.

I just took the engine apart to check the cylinders out, and I had a few questions about how to tackle this engine.

Firstly, what all do I realistically need to do? Before I lost the alternator (reason for rhe initial teardown of the bike), I was able to ride the bike but I had a lot of backfiring on one side, enough to burn holes in the pod filter. I'm not sure if the carbs were the issue, the pods, or something in the valves or timing - and I don't really know what to look for.

Second thing, I was looking at some of the threads here and elsewhere about fuel onjection and it seems really expensive. I've read that pre-2014 BMW F650GS has a basically standalone ECU and a conventional, non-CANBUS harness - and both the ECU and throttle body assembly are pretty inexpensive used. Is this a system I could relatively easily retrofit in place of my stock carbs? My other bike is fuel injected and it's so, so nice.

Finally, what are some of the best engine paints you guys have found? I think I'm gonna go for a blacked out engine.

Thanks a bunch, and sorry for the wall of text

 

[650Skull]

Welcome Nercitar,

Pretty broad band to answer. A good set of carbs, (properly rebuilt), and an electronic ignition will make an XS650 run nicely.

Basically on the engine, with the head and barrels off, you need to check the con-rods for play and if they are in speck then the bottom end should be ok. a hone or re-bore and new pistons, after measuring the pistons and bore inspection to determine whats in speck. Need a front cam chain guide. They de-laminate with age so need to be replaced. New cam chain and decarbin the valves and lap with new valve seals and check the guides, if worn replace.

Test and determine if its your rotor that is at fault in the charging system. You have a mechanical regulator and this can be reset. there is a lot of information on replacing charging parts with rebuilt rotors and automotive regulators and 3 phase rectifiers that makes the XS system reliable and reasonably cheap to do when looking at alternatives like PMA's and SS Reg/Rect.

Give more info on your capabilities and where your at to get more pointed information and post tons of pics because we are illiterate and need pics to understand

 

[jpdevol]

I concur with 650Skull on the carbs. I love EFI too, but a well rebuilt and jetted set of Mikuni BS38 carbs (that you have) will perform surprisingly well; warm-up with choke off in a few seconds, good driveability. I'd go that route first before attempting EFI.

 

[Nercitar]

I am in metro Detroit, I have a great mechanical aptitude but next to no experience with this sort of work.

I appreciate the advice regarding the carbs - I just put a rebuild kit into both, and cleaned them up inside and out. Once I get my engine and electrical in order, I would be just fine running them if they have a good reputation with those in the know. I'll have to learn how to adjust them.

I also appreciate the pointer about the cam chain guide - I am sure I would not have considered that.

As far as valves go, are they easy to lap? My local Auto Value has a valve lapping tool that basically looks like fat stick with a bevel on one end... so simple it makes me nervous! My valves are covered with nasty, tan crusties, I haven't cleaned them yet and I hope they're not messed up.

Anyway, it sounds like I need to get some calipers. I've got measuring to do... My cylinders do look a bit glazed, but not really scored or anything. I was thinking I'd just hone the bores and re-ring the pistons but maybe I better pay more attention to the details.

 

[jpdevol]

I just put a rebuild kit into both, and cleaned them up inside and out

There are some rebuild kits that are subpar and will not give good results. The accepted standard here is genuine Mikuni jets and fuel screws where possible, JBM diaphragms if needed on original slides, genuine floats if needed. Excellent "carb guide" here in Tech section.

 

[Wingedwheel]

Welcome Nercitar, just NW of you. Lots of great guys and info here just ask your question with enough info and chances are you’ll get an answer.

 

[Nercitar]

There are some rebuild kits that are subpar and will not give good results. The accepted standard here is genuine Mikuni jets and fuel screws where possible, JBM diaphragms if needed on original slides, genuine floats if needed. Excellent "carb guide" here in Tech section.

Well, here's hoping my kits weren't trash. Luckily, my floats and diaphragms were good, and I saved all the original jets and screws just in case I needed them. Hopefully at least my gaskets and seals are okay, if nothing else!

 

[Nercitar]

Welcome Nercitar, just NW of you. Lots of great guys and info here just ask your question with enough info and chances are you’ll get an answer.

So far so good, I hope I am providing enough information.

Nice to see somebody is so close, by the way! 2 wheels down

 

[650Skull]

Before buying any parts it pays to ask first. There are different suppliers where cheap quality parts are available.

Valves can be cleaned on a wire wheel.

Carb kits as mentioed can have generic parts that aren't suited to the carbs. between 74 and 79 the BS38's have 3 different needle, needle jet and jets setup so its important to make sure the carbs are identified for the right jet/needle set up.

 

[Jim]

First, welcome to the forum!!

Have a read here. I wrote that to help out a guy who'd never put an engine together before.... rip Robin.
It won't answer all your questions, but we can fill in the blanks.

As as been said above, you'll need a new cam chain guide. Someone here (drawing a blank here guys... help me out) sells a nice one.
New chain. Get an OEM chain....
A fair bit of what's out there is junk.... I'm lookin' at you MikesXS..... ask here before you order stuff. Someone here will know where to find the best products.
Carb kits are mostly junk. Look for OEM Mikuni (damn.... another blank... ) brass.

Pics man.... we need more pics!!

 

[Jim]

Gary Hoos for the front guide....
https://www.xs650.com/threads/new-front-guide-stopper.56531/

Niche Cycle for Mikuni brass.
http://www.nichecycle.com/ncs/

 

[jpdevol]

If the carbs are '79 BS38, you'll want to get 27.5 and 30 size pilot jets to get the "driveability" I spoke of. Just so happens, I just received an order from Niche that Jim referenced for '79 BS38's: attached

 

[jpdevol]

Also Hoos Racing on the cam chain:

447 Motor Cam Chains 74-84

Part# 02106 (FACTORY YAMAHA) $65.00

Note: gotta order via email - no shopping cart

 

[Jim]

Finally, what are some of the best engine paints you guys have found? I think I'm gonna go for a blacked out engine.

POR15 and VHT are the two best engine paints I've found.

 

[jpdevol]

LOL. At the risk of info. overload: regarding valve lapping; if your seats are in reasonably good shape they're no harder than average. Of course you'll need a dye to check seat location. The stick with the suction cup is the tool to try - it takes practice. Just garden variety lapping compound: Permatex ok (I use Goodson). If the seats won't clean-up or are in wrong spot, I use Neway cutters from Goodson Tool. Pic of marking dye attached

As far as valves go, are they easy to lap? My local Auto Value has a valve lapping tool that basically looks like fat stick with a bevel on one end... so simple it makes me nervous! My valves are covered with nasty, tan crusties, I haven't cleaned them yet and I hope they're not messed up

 

[Nercitar]

If the carbs are '79 BS38, you'll want to get 27.5 and 30 size pilot jets to get the "driveability" I spoke of. Just so happens, I just received an order from Niche that Jim referenced for '79 BS38's: attached

Awesome, awesome resource. Thanks!

 

[jpdevol]

I forgot to ask about your tools. Two you need some variation of; a correct size chain breaker/riveter for the cam chain and a right-sized valve spring compressor. There are variations available, this is what I use:

https://www.pitposse.com/pit-posse-chain-cutter-and-riveting-tool.html
https://www.denniskirk.com/motion-p...d-18mm-adapter-08-0702.p284844.prd/284844.sku

also popular, but twice the price of Pit Posse
https://www.denniskirk.com/motion-pro/chain-riveting-tool-08-0058.p28350.prd/28350.sku

 

[Nercitar]

Thank you to everybody. I will pick up some tools and get to work as budget allows, and I'll do my best to post pics!

 

[Wingedwheel]

There are also ways around some of those tools but a very important one is a JIS screwdriver set. About $16 on Amazon

 

[Nercitar]

I've heard about the JIS screws. I was thinking I'd just replace them all with allen screws to be honest. I got this bike as a project from my dad, and he had already done so for all the carb screws.