Jet Needle question

[wingedwheel]

'78 750A. I received my carb kits today and I noticed a difference between the new and the one I removed. you can see by the pic there is a difference. The service manual shows a needle similar to the new one. My question is about the old needle. Is that what was installed at the factory?

 

[amc49]

....................I for one do not know

See if the new part has the number on it, some do and that might be an indicator. Same with old part. You'll be breaking out the magnifying glass.

 

[wingedwheel]

Amc49, I've gotta break that out no matter what...... I will use your suggestion however. Thanks

 

[dirtdigger]

Does the bike run? If it ran with the old needle then it is probably original. If the original one fit and ran then the new one definitely wont, it is way too long. This style of carb on the non auto bikes used a single slot needle, only the old round top carbs used multi slot and they are not interchangable. I am not 100% sure what the autos used for a needle but I would have to guess they used a single slot like the non auto carbs did

 

[wingedwheel]

dd that's why I asked the question. However the factory manual shows a multi slotted needle and that's what the kit came with. I wondered about that after looking at them. It will fit in the linkage arm and the new main jet is different so I was hoping that would allow for the slightly longer needle. the manual says to set the needle in the middle slot for 76-77 models, however it doesn't say about the 78 model. that being said there are 5 grooves so I'm assuming the 78 would be the same? It was the length that got me wondering. Everything else in the kit is spot on fit. Bike did not run, it sat for 26 yrs and the slides were basically so gummed up the throttle wouldn't work. It was a little scary for me pulling them apart. I'm definitely taking my time rebuilding them.

 

[amc49]

This X2..............

'If it ran with the old needle then it is probably original.'

With a needle change like that you are likely needing the needle jet that matches it. Check yours to make sure it is correct for that needle.

Normally wildly different lengths like that scream wrong part. The parts catalogs HAVE shown multi-groove needles before when there were none there and I've seen drawing discrepancies on lots of other parts too. Sometimes even though model specific the pics can get a bit generic.

The not mentioning '78 model may be because Honda right around then began to put out emissions carbs with locked idle screws and needles with only one position.

I'd use the middle slot and if it runs like crap be quick to suspect wrong parts there, that will be night and day noticeable.

Again, check the needle jet, they always match to the needle used.

 

[wingedwheel]

amc49, I did change the needle jet and it appears to be ok but like you said, I'll have to wait until I run it. The part# on the original is 18B, the new one is D432. Where is a good source for part #'s? It would be helpful if I could compare the #'s on several of these parts. I started with a single carb before I dove into the other three. I don't know why carbs make me nervous, I've rebuilt plenty with no issues but I know if I miss one thing it's a do-over

 

[dirtdigger]

If they are not damaged why change them? Leave the stock needles and needle jet there and be done. No point in causing a self inflicted running problem. All the 750 PD style carbs I have ever seen have a 1 groove needle, only the old 750 round tops had multi groove needles. Leave the original parts in and run it.

 

[amc49]

X2 and the man has a very definite point. I feel the same way but not as sure about the SOHC carb parts as he. I suspect multi-groove stuff as the early type carb parts too. PD stuff being a cheapening and emissions tilted new wave design. They showed up around the same time as welded in baffles, efforts to stop owners from modding things that raised emissions again.

Playing around with the needle/jet is one of the most messed up things one can do, I STRONGLY suggest using the single slot part if that is what came on it.

The length of needle there alone screams wrong part and the slides may not even close all the way if the needle sticks in the jet. They should never touch and even sticking the needle can damage it as any scratching of the surface is BAD.

 

[amc49]

You gotta READ the FSM.

I went back and looked at the one I gave the link for earlier, in section 13 it clearly gives a spec of a line drawn through the needle clip position setting for a '78, meaning it is non-adjustable, the '77 it refers to '76 with an arrow to show you copy what is done on '76.

As well, when you go to further carb rebuild info they also say to use the middle clip position but ONLY again on '76-'77 and '78 is LEFT OUT. Think about why that would be so.

The parts breakdown says to make sure you use the same needle jet that goes with that needle as the two types are matched to the needle jet hole size too, the needle jets cannot be mixed with the different needles as they are incompatible.

The '78 uses a ONE groove clip. The carb body should say 'PD43A' somewhere on it.

You likely have '76-'77 multi-grooved needles there. They may NOT work in a 43 carb at all since they were intended for the 44 series (again, read the FSM!). The slide up/down location point may be different and why the needle length is off, now you may need slides too. There is often a 'choke' built into the needle jet top too and if so it would be critical on the automatic to have the correct one if the later carb is leaner like I suspect. The choke if present induces a stronger first fuel pullover signal to the needle lower down and has everything in the world to do with how the engine reacts at first pulling away from idle. You must also bear in mind that the main carb body has the main air jet that matches to the needle jet and there is a whopping change there from a #150 to a #200 'standard air jet', the one I am talking about, so using the earlier needles and needle jets may well clash with that as the entire power range is based on not only the main jet lower down but the air jet too, it by the size shapes the entire upper power curve. If you want to go to carb hell then messing with that main air jet can be the best way to get there fast, you pretty much need a wideband O2 sensor setup and the skills to diagnose with it to sort that out.

See how much trouble we can quickly get into with incorrect parts? And we haven't even started yet.

 

[wingedwheel]

amc49, you're giving me some great info. I'm just wondering why every kit I find which says 76-78 750A it shows a grooved needle. I saw everything you mentioned in the manual and wondered why there was no designation on setting the needle for the '78 on page 13-4. I also noticed the issue date at the bottom of the page was Dec '77. would that have any significance?

 

[amc49]

No. By then they would already have likely known any changes on next model year being as they were just like cars and the year model released around Sept. of the previous year.

You just have to figure a lot of that stuff out by putting various facts together, they don't literally spell it out for you, and what I do on things all day long. For instance, my conclusion it was all done to stop people from messing with the bikes to increase emissions. There is no evidence there other than what I put out but that means absolutely NOTHING. It is plain enough to see where they are going with things once you watch enough.

The reason you don't find the other single clip needle is likely there were less of them made (2 years production of one and only 1 of the other). The aftermarket will make the early ones going after the tuners market, who wants a needle that won't adjust? The old selling adage...........don't give them what they need, give them what they WANT.

Two big reasons there. The fact you need the correct needle jet to go with it doesn't impact that, that's YOUR problem, not theirs. Of course they won't tell you that, it would scare you off buying the 'trick' part. ALWAYS look for the money and the motive and you can't lose. If I had a dime for every mis-advertised part to increase sales there were you could call me Donald Trump.

 

[wingedwheel]

amc49 I'm thinking if what you're saying about emissions is correct, wouldn't that also mean that once the bike was no longer in production the need for the single clip needle slowly went away so I should be able to use the one in the kit with only the emission impact? In any case if I can't get the stock needles I'll just have to deal with any issues that may arise. That being said, two carbs down and two to go. here is what I'm working with... I've done 3&4 this is what 1&2 look like. 3&4 were just like that.

 

[dirtdigger]

You also have to remember that the auto carb is smaller then the standard tranny model. They are not the same carb....same style but definitely not the same. These pd carbs are indeed set up more for emissions/ lean....one of the reasons they added an accel pump and made the pilot jets press in and the needles non adjustable...so the owners couldnt mess with them But the aftermarket worked around that by offering jets and started selling shims to change the height of the needle.

 

[amc49]

Until a fit up with the adjustable needle and its' needle jet is done with a slide to see if the slide closes 100% all talk is just that. OP keeps walking away from the needle too long issue like it is nothing. Also ignoring the difference in air jet.

No way here are we talking about something as minor as emission impact, rather talking about a carb that works or is totally unrunnable. If the earlier slide was modded to accommodate the longer needle your slide will not work with your earlier parts.

(edit) Just went looking at parts at Partzilla, the slide shows to be a different part number from '76-'77 to the '78 too, so, not looking so good there.

 

[wingedwheel]

I'm not ignoring the longer needle, actually the first thing I did was check the slide travel when I put it back together. It appears to be closing and from all info I can find that part is obsolete, therefore NLA. I guess all I can do at this point is put them together and see what happens. I did keep all my old parts in case I have to put them back in. Problem with all this is there is so much to do on this bike it might be a while before I can actually run it to find out.

 

[wingedwheel]

Another thing I want to check is the length of the new needle compared to the old when installed on the first groove. I'm just trying to stay productive without grinding to a halt because one part isn't right.

 

[amc49]

Not trying to hassle you, yours and do what you will.......................the problem being the one wrong part messes up way more than just one, and what commonly happens when doing carb work. Been there a 1000 times. When one part gets modded often an entire stream has to mod with it. Don't overlook that air jet change, it will tilt your fuel/air a whopping amount and now none of the standard jetting will likely work, so now no clue as to where to begin jetting. Not to mention if one needle is a single taper and the other a double taper............................the differences that kill you often cannot be seen.

Luck.................

 

[wingedwheel]

Not taken as hassling. I asked for advice and that's what I'm getting. I just can't believe someone else hasn't run into this or perhaps they have and it's just not a common thing. the replacement main is the same #. I know you're not supposed to re-use the needle if you change the mains but I may have to. If that's the case should I re-use the needle holder also?

 

[dirtdigger]

A question that was never answered, why do you think you need to change the needle? Just because it was in the kit? If non of the needles are bent or damage dont replace them. There is absolutely no reason to replace the needles and needle jet unless there is damage. All you are doing is introducing a problem into a system that you dont know if it ran well in the first place. Reuse the needle and needle jet and clean the carbs and replace gaskets and float needle if you have them. Get the thing running, then if you have problems with running issues look into it then. You are causing yourself head aches trying to replace parts that are fine and no reason to be replaced and possible causing you running issues by introducing an incorrect part into the mix. Clean carbs, stock jets/needles, new gaskets/orings, running adjust from there=done. Not trying to be a jerk or anything but trying to save you countless headaches. I have NEVER replaced a needle in a stock carb in my life. Especially on a stock motor with stock carbs. Replace the soft parts and get on with the build and get it running.