Topic: 1972 CB500 Restoration, Carb question/problem

[IrocRuss]

I'm new to the forum.  The only reason I really signed up is I'm doing a restoration for my wife's cousin, who knows nothing about motorcycles and didn't know where to start (he's not a mechanical guy).  Jeff (bike new owner, wife's cousin) inherited the bike from his uncle who bought it new in 1972. Bike was last ridden in the mid 2000's.
 I have been around working on and riding motorcycles for 45+ years.  I probably had 6 or 7 SOHC 750's in my 20's through early 30's when I got married.  More recently I'm into cruisers.  Anyway Jeff knew my background and asked for my help to get this bike back on the road.

I really don't have a lot of time to go into detail of the whole process, the whole bike has been gone through and is back together.  I am at the point of trying to get the bike going but having problems.  I originally wasn't going to do a total rebuild of the carbs, but found pitting in one of the float seats.  All of the Orin's were rock hard and there was some light corrosion, in carb bodies, so I opted to do a total rebuild.  The carbs were initially soaked in Berryman Chem-dip #0996 and then placed in an ultrasonic bath.  After rinsing and checking all orifices were clear, I assembled them with all new jets and Orin's from Rusty Riders off of Ebay (kit was specific to 70's CB500 and 550). Carbs were statically synced, floats set to 22mm.  As a side note, that I've already fixed, 3 of the 4 carbs overflow tubes were split.  When I was assembling the carbs, I noticed that some of the parts looked different, but they all had the correct jet numbers.  I assumed everything should work fine, but I'm having issues.  The bike has spark (all new plugs), no more leaking out the overflow tubes, the float needles seem to be holding (I've heard of many having problems with aftermarket valves and jets).  But the bike only loudly backfires.  I pulled the plugs and they were dry, looked in the cylinders with my bore scope and it looked a little damp but not like it's flooded.  I was going to try to clean and replace the pilot jets with the original OEM #40, but I have seemed to misplaced the old parts from Carb 1 (getting old and senile).  I just sent a message back to the Ebay seller I got the kits from with a picture of the difference in pilot jet lengths (also attached here) asking if maybe got the wrong pilots in the kit.  I would think the length would affect the jets operation as it would affect the liquid head pressure.  Any experts out there that may have an opinion or advice?

[HondaMan]

This is a story that is OFTEN repeated: I have had to answer it here and in my e-mails almost 40 times since last year.

The parts you got were NOT correct ones, period. There are many vendors out there, selling incorrect parts. Many of the parts are Keyster brand, which means the needles are 25% too thick and the mainjets are both undersized diameter (so they will not seal in the passages) and their inner tapers are different, so they run about 7%-10% too lean. couple that with the too-big needles, and there isn't enough fuel to the engines to even make them idle, let alone run well.

First thing: you need the proper pilot jets or it will not idle. They will be size #40, get the genuine Keihin in the same length as OEM (I get them at JetsRus.com).
Next: try to find those OEM needles, they are not widely available. They don't wear out, either, and the needle jets for the Keyster have bigger thru-holes, so they don't work with the Keihin needles, either. Try to find those OEM needle jets.

The Keyster float valves work OK, though, except the springs are too stiff: to fix this just raise the floats about 1mm more than stock to help deepen the float bowls.

Finally: once it is running again, pull out the spark advancer and cut off at least 1/2 turn from one of the advancer springs, if not both: they are heat-annealed now and mush too soft, advancing timing WAY too early, like 1600 RPM at full advance. This makes the carbs spit back and makes for wet, fouled sparkplugs by the box full. It also removes about 25% of the low-end torque (below 4000 RPM) when riding.

[IrocRuss]

Hondaman thanks for the reply, that's exactly what I was looking for.  It really ticks me off I lost the parts from 1 carb, I usually save all of the parts for this exact reason.  I did notice that the jets looked different, but the needle looked the same, length, taper and width.  Do you think if I replaced the main and pilot back to OEM, I could get by with the aftermarket needles since they look the same. This is the kit I bought:
https://www.ebay.com/itm/FOUR-NEW-Honda-CB500-F-Four-Carb-Rebuild-Kits-Kit-CB500F-CB-500-Carburetor-Jet/360795207303?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2057872.m2749.l2649

I included a couple of the before pictures, only ~6700 miles.

[IrocRuss]

While I am waiting to get my new correct pilot jets there from JetsRus, I decided to check somethings over to make sure I didn't have some other issues.  FYI, this bike was sitting for 15 years and I don't know the status it was in then.  I checked points, they looked OK, 1-4 was a little tight, I re-gapped at the minimum 0.012" since that's what 2-3 were (left those alone).  Checked static timing, 1-4 was off a bit so I readjusted to right on.  But thing I didn't like was the plate was adjusted all the way clockwise to end of slot.  When I check 2-3, timing was off quit a bit more than 1-4, I had to run this all the way to the end of the slot (counterclockwise), but still off a bit.  The "F" mark is about 1-2 line widths off of the timing mark.  Any comments on this?


Checked compression cold, was a little low  but all within 7% of each other.

I removed carbs and setup on a stand to test float levels and how well float valves hold.  Carbs 1+2 level seems a little high, and not immediately obvious, they both leaked out the overflow after 10 or 15 minutes.  I removed carb bowl #1 and made several observation that concur with what HondaMan said in earlier post.
On float valve, needle looked OK, orifice is same diameter (#50 drill, 0.070") as OEM, spring a little stiffer, but biggest issue was seat had burs in the bottom of hole and the actual seat had tool bit chatter.
The aftermarket main jet looked identical in the entry and exit of the orifice, and were the same diameter, #60 drill size (0.040") orifice.  The problem is that there was a brass chip in the aftermarket orifice blocking ~25% of the opening (see attached picture, zoom in to bubble).  Obviously some quality control issues.  I haven't opened the other 3 carbs yet.

I'm attaching some pictures concerning my comments.  The float levels look high, especially on 1&2, anyone have a feel of where level should be at.  I used the back of a digital caliper to set the float levels at 22mm, I'm getting a float gauge from JetsRus to double check levels and reset to the 23mm. 

I'm in the process of cleaning original jets, but I've found some are pitted.  I may be stuck with trying to cleanup the aftermarket jets I have. 

[bryanj]

Points gap needs to be 0.35mm, that will move plate back.
Points need to be clean and flat plus take time to get gap and timing spot on, it takes time and patience as plate moves a bit altering gap.

That is an early K0 you have and i am compiling a list of numbers and date so would be gratefull if you would pm me the build date and frame number from plate on headstock plus engine number.
Thanks
Bryan

[Scott S]

 I would put the stock needles and emulsion tubes back in. Same with the main and pilot jets. Genuine Keihin main and pilot jets are available at JetsRUs.

[IrocRuss]

Points gap needs to be 0.35mm, that will move plate back.
Points need to be clean and flat plus take time to get gap and timing spot on, it takes time and patience as plate moves a bit altering gap.

That is an early K0 you have and i am compiling a list of numbers and date so would be gratefull if you would pm me the build date and frame number from plate on headstock plus engine number.
Thanks
Bryan

Hey Bryan, when I looked up gap specs in manual (0.30-0.40mm), my initial intension was to set it in the middle, which is 0.014" (0.35mm).  Point gap was filed first and cleaned before checking.  When I went to do it, I checked 2-3 first (because it was already there) and it was 0.012" (0.30mm).  I wasn't sure if smaller gap or bigger gap was better, so I left it there and adjusted 1-4 the same.  I will go back and set to 0.014" and see if that gives me enough play in the slots to get the timing right.  Seems like 0.002" is very small and wouldn't make much difference, but I'll let you know.

I'm new here, wasn't sure how to PM you on this forum, so I included pictures of my serial numbers.

Thanks, Russ

[IrocRuss]

I would put the stock needles and emulsion tubes back in. Same with the main and pilot jets. Genuine Keihin main and pilot jets are available at JetsRUs.

I have all of the stock emulsion tubes because they weren't included in the carb kits.  I had all the other old OEM parts bagged and numbered and somehow managed to loose a bag, so I'm short parts.  The whole reason I bought new kits was there was pitting in the float seat on 1 carb.  I haven't looked at all of the old part after cleaning, but one of the needles I looked at is pitted, not sure if I want to reuse this.  From what HondaMan says, you can't buy OEM needles anymore. 

When I talked to Mike at JetsRus, I specifically asked him if the Pilot Jets #99124-076 (not sure about main jets) were factory Keihin jets and he said no, they are aftermarket, but designed to Keihin specs, so for now I ordered the one I'm missing to compare to the OEM ones. 

This isn't my bike, it's my wife's cousin who know's little about motorcycles.  He bought it from his uncle's (the original owner) kid who inherited bike, and thought you could just put gas in and go after sitting for 15+ years.  I've probably got ~$1000 invested in parts and he doesn't want to spend much more.  Jeff (wife's cousin) is concerned that he is going to have more invested than bike is worth, so I'm trying to keep cost down as much as possible.   Off course the bike has to be running well to sell it anyway.  I know decent SOHC 750's can be worth quit a bit, are the 500's gaining value if in good condition?

[bryanj]

That bike in UK would sell for £6-7000, it is an early K0 but not one of the first run which would be even more.
I have some odd original carb bits but its posting to US! One thing missing is below the side panel badge on each side shoul be sticker saying:-

Honda Motor Co.
Tokyo Japan

There was never a part number for these but i had some made a long time ago.

To PM click on my avatar and you should see send a pm there.

Hope you get it all sorted they are nice bikes

[HondaMan]

I have to admit to not knowing that brand of parts: they are also kind of pricey (to me, as I'm a cheapskate...but correct is correct...).

Can you read the number etched around the top of the [Keihin] needles you have? I have an odds-and-ends collection of needles from the years of rebuilding these carbs, could look thru to see if I have one that matches?

The primary cause of troubles with the Keyster needles is their lean-ness: they are so big in diameter that many of them will not even drop into the OEM Keihin needle jets, unless they are pretty worn. That's a lot of difference! In reverse, running the OEM needles in the Keyster needle jets makes everything exceedingly rich, because the Keyster needle jets don't close up with the stock needles' diameters, so they lose their metering ability altogether.

[Deltarider]

That bike with its 4 OEM exhausts is certainly worth to spend some money on.