Black spring vs. sprocket adapter vs. jackshaft

[chazdaddy]

Hello Dave,

Sorry, been away from my computer helping my 89 year old Mom.

The link to my post to thread "getting most from your 2.8" is what I would say again. Also, the link in the post to the micro drill set worked for me, but I linked it again. Nice set, and less than $15 shipped to your door, a good deal IMO.

Your link to OldMiniBikes drilled jets is not the one, will not work, too large. The jet that works from the 6.5hp Clone is the idle jet. The idle jet is the black plastic jet. You want a stock one, not drilled out. You can get these for less than $5, but shipping may be expensive.

You will have to drill out the brass main jet with a micro drill. If you drill it out too large it will be trash. As I mentioned, may be able to get these from Honda, but I have not tried to buy one yet. If you ruin the main jet, may be looking at buying another carb, so I suggest waiting on this mod.

I would clean the carb, install the green clutch spring, and see how it runs. I got mine to run really well before I ever rejetted the carb, so you may not need to do it anyway. My grandson's DB30 runs very well with stock carb, black spring, sprocket adaptor, and 78 tooth rear sprocket. For his, rejetting carb would help huge on a cold day, but on a hot summer day, probably not a lot of difference. I like to ride this mini, but with jackshaft would be better.

Good luck, have fun. Cheers :thumbsup:

Mini Micro Drill Bit Set #61-#80 Swivel Pin Vise Combo - Amazon.com

 

[Dave.]

Thank you for the follow-up Chaz. I have the drill bits on order. Will wait on any drilling and see how it goes. I need some rainy weather because the boys are having too much fun with the new mini bike, which they both like better than the old one (6.5hp). I'm guessing maybe partly because it's so much more comfortable in the yard and woods. I think when the jackshaft goes on, we'll all be fighting over it.

If the carb is clean, and the ports open, is it the main jet restriction which causes the thing to want to be on 1/3 -1/2 choke all the time? If not on 1/3 choke, it will want to quit right at the start of throttle-up from idle.

It seems to idle ok, so I would expect that jet to be ok as-is, right?

There are a number of threads with similar problems and the suggestion is usually to try to get a richer mix. Just not sure if it is the main or idle jet when the problem is right at the beginning of throttle-up.

 

[chazdaddy]

It's the idle circuit, which is the idle jet (black plastic jet) and idle jets in throat of carb (between engine and butterfly, maybe 3 or 4 very small holes).

Report back when you have stiffer clutch spring installed. My grandson's won't hardly run with the stock spring, but runs great with the black spring (same carb, no changes to carb).

The clutch engaging at higher rpm allows engine to get past lean idle condition that causes the problem at take-off IMO.

 

[Dave.]

Update - clutch engage rpm

Update...

-Still- waiting for the spring and jackshaft... Unfortunately, it's late enough now that I won't have time to work on it before the weekend. Next two weekends are booked.

I did get a chance to clean the carb well and noticed no difference, but without any change in the jets, that was kind of expected. I have the drill bits now but will wait to try the spring first.

I also received the Hardline tach and checked the clutch engagement rpm. Only about 1800-1900 rpm. It idles about 1500. I expect the spring--even the green one @ 2500-- to make a big difference. The MaxTorque on the other mini engages about 2200-2300. 1900 is really low.

 

[Dave.]

Green clutch spring - update

Finally got the green spring in the mail yesterday from the rip-off USPS so-called 2-day Priority Mail. What a scam they run...

Anyway, I installed the green spring in the clutch just now. No other changes.

The engagement RPM is now about 2100-2200 on my DB (not 2550 as the description says). And this according to my tach, which could also be off, but I doubt it, based on measurements I took on the other mini bike. The original DB spring was engaging at about 1800-1900 RPM. Maybe the shoes are worn, making them lighter.

Based on this information, I was say that the -black- spring is indeed the correct one for the DB clutch. I suspect that it does not engage at 3100 RPM as described, but likely lower, and therefore would the the proper choice. YMMV.

Take-off performance with the green spring: I noticed only a very slight improvement. If you changed the spring and didn't tell me, I probably would not have noticed any difference. That's disappointing. But I have the jackshaft to try out next.

 

[ProMod]

Sorry again Dave that your order was delayed. I really wish it could have gotten there sooner.
Not only did the shipping take longer that it normally does, but we also had a tech problem with our Internet service provider last week. All fixed now and things back to normal, but it did set us back a few days on getting orders out. I apologize to anyone else who had there order held up a few extra days last week.
I do have to say though that we have had pretty good service from USPS compared to the other carriers we have tried. I have talked to other companies about there shipping service preference. Everyone has different experiences. It seems that it depends more on your location (either where your shipping from or to)) to how good the service is you get. Or even if they can actually supply a 2 day shipment. The services at the different post office locations are not all equal. As with all the other carriers. Not a perfect world. Anyway... not to get off on a rant about that.
Just glad your stuff showed up OK.
As far as the clutch springs go.The RPM spec is more of reference point to use when tuning with the different spring tensions. I don't think the clutch manufacture can 100% say what the spring will do in every clutch. Especially if your using it in a china copy of there clutch. You also can put the front tire against a wall and check the holding rpm on your tach. But it may not be the same actual rpm full engagement accrues when riding. To many variables come into play. So it's safe to say the green spring is a little stiffer and the black spring is a lot stiffer. Some riders may have had good results and like the black spring. But it does cause a lot more slippage, especially when used with the small engine.
This may cause problems and overheat the clutch in some cases such as..
If the bike is doing a lot of stop and go riding on grades,
With a new rider who may be timid with the throttle taking off.
Or heavier riders with the stock engine and gearing.
IMO when it comes to the black spring and the larger engines. I prefer it over the stock spring hands down either with a modified or bone stock engine.
But not all riders weigh the same or ride the same. Some only ride off road and in hilly terrain, others just want to go down a flat paved road to see how fast they can go.
Playing with different gear ratio's and clutch tunning are a simple and fun way to get your bike to perform to your needs. I'd say get your JS system installed and see what you think before tinkering more with the black spring and the clutch. The lower gearing takes a huge load of the clutch and changes things quite a bit. The green spring is just another tunning enhancement. In a lot of cases these bikes are ridden around quite a bit with the stock gearing and the clutch gets over worked. The stock spring looses its tension due to being over heated. A simple clutch tune up involving a drum and shoe cleaning, bushing clean/ lube, and a new spring brings them back to life.

 

[Dave.]

Jackshaft u

Thanks for the follow-up, Brad. I guess I'm just not lucky with the USPS. I'm convinced that the "Priority Mail" was mainly a (insanely successful) marketing ploy to pull in more money. Since so may packages are now PM, and have no guarantee of delivery time, the USPS can say whatever they want, and do whatever they want. You cannot even buy postage online unless the package is at least PM. And heaven forbid there is a digit wrong in the zip code (that happened to me this year). They do not (WILL not) read the rest of the address, and the package will simple go in circles... Anyway, that's my rant. Upside is they still have Saturday delivery. For now.

I did get the jackshaft installed today. It was easy as pie, and all the parts fit perfectly. Even no alignment needed for the sprockets. Everything included, and I do mean everything. Very nice. No trips to Ace.

One suggestion on reinstalling the metal chain guard. Instead of turning the bolt around and installing a nut on the outside (so the chain doesn't hit it), just put a spacer or a couple washers between the fender and the bracket to effectively shorten that screw. In my case, the (reversed) bolt head was still protruding too much into the chain, so easily fixed with washers and the bolt heads are then in the same direction, too.

Performance... Very good low end now. Can start on hills now, and accelerate up a hill. Top speed 20mph @ 4400rpm. For off-road (in the woods) this is plenty. The green spring may be helping it out here, too, don't know. However, now the engine is better able to deal with the leaned out mix coming from the carb. It doesn't stall so easily on take off.

Re: green spring: I chose this one particularly because of the young rider who is on and off the gas all the time. This would not be sufficient to make this DB rideable, IMO. Maybe with the black spring. Maybe with the carb jet drill-out. I'm not sure if I will do that one. The engine seems to run well at 1/3 choked. I don't know if that is damaging or not.

 

[Dave.]

Also, don't need to mention since almost everyone knows this but for newer folks: the jackshaft is the very high quality typical of ProMod products. Such pretty welding...

 

[chazdaddy]

These little clutches work great for what they are and especially what they cost. However, they are high maintenance IMO.

My son-n-law is the original owner of Honda Z50R that's approx 30 years old. It has been rode hard and put away wet many times, it's been abused, and it still runs pretty well. If instead he got a DB30 when he was a kid, it would have gone to the landfill many years ago.

That's not to say I like the Honda better, actually I like the DB30 much better, especially for the cost.

Same goes with the cheap Max-torque clutch. How it operates depends upon some variables, that would have been engineered out by Honda, but at additional cost. One big variable is oil or grease in the clutch. I like a little oil in mine. Some of the extra oil ends up on the shoes and inside the drum and allows the clutch to slip more. If you keep the clutch oiled the same, you will get consistent performance, anyway that's been my experience.

I oil the hub bushing often when I come in from a ride while it's hot. How smooth it operates and rpm engagement really changes when it starts to go dry.

Not to say you should oil your clutch, some people have trouble burning up clutches, especially as you get more HP. But you might want to experiment with it. I am just saying it works for me, smooth consistent engagement.

The downside is you have to do maintenance often. I actually drilled a hole in the plastic clutch cover so I can oil the hub bushing without taking the cover off. :thumbsup:

 

[toomanytoys]

I have a questions, I didn't real this whole thread...

Instead of going through all the work to make the 97cc DB run better why didn't you just replace the motor with a 3.5 or 5HP briggs or tecumseh? I've have rode a ton of 3.5HP bikes, and they were all more powerful than the China DB motor.

 

[Dave.]

Say, Chaz, I pulled out the black plug on the mixture screw. Did you play with the mixture at all before you drilled the jets? Seems the low-speed end is what needs to be tweaked (to run well with choke off), and that would do it, right?

 

[chazdaddy]

Hello Dave,

I think I know what you are describing. Anyway, this is different on different carbs. On some, you can adjust, others it's just a jet that is screwed in on the side of the carb (not adjustable). Take it out and see what you have, report back. :shrug:

 

[Dave.]

The screw in there turns -very- easily. If it's just a jet, then these things are loose underneath the black plastic plug (which may or may not fit the hole well enough to push on the screw and hold it in place).

I'll check it out tonight: count the turns in so I can put it back where it was, and then take it out for a peek.

 

[Dave.]

It's a needle

On this particular engine, under the black plug is a needle, not a jet.

But there is nothing holding the needle position now. No spring, or tight threads or anything. Well, a tiny little o-ring which seems worthless. Somehow, the black plug held the needle in position. Now, when I rev the engine, the needle turns itself INWARD (clockwise). Go figure.

I lost the exact original needle position. But before I lost the count, it seemed to work best turned in about 1/2 from the original position. That looks to be about 3 1/4 turn out from bottom.

However, this still does not solve the problem with the engine coming close to stalling (or stalling) when I give it gas out of idle. It seems to make it better but not a lot better.

Turned all the way in or out, the engine dies, as expected.

So maybe I can use some blue Loctite on the threads and put it about where it needs to go, and still be able to adjust it without it moving by itself.

 

[Camjamsdad]

Could try carefully applying a little Teflon tape on the threads. Locktite is a little overkill

 

[chazdaddy]

Hello Dave, just want to make sure you don't have this jet/ needle confused with the idle jet. Best I can tell, you adjusted it and doesn't really make a different anyway. Also, wasn't running right before you took it out, so not sure why you want to put it back the same? Maybe try screwing it in just enough to keep it tight and see how it runs. :shrug:

 

[Dave.]

The idle jet is the black plastic jet with metal insert, that lifts (not screws) right out when you remove the large black plastic idle adjustment screw. These are on the top of the carb.

The needle (not jet) I'm talking about is on the right side of the carb as you are sitting on the bike. It was underneath a semi-permanent, black plastic plug. I drilled a small hole in the plug, then levered it out with a tiny screwdriver.

This needle has a black o-ring on it, just as the black plastic idle jet has an o-ring on it. The needle I'm talking about is brass. When it is screwed in all the way, the motor will not run at all. When it is screwed out to where it was after I removed the black plug, it runs, but not great (tries to stall coming out of idle.). It wants to have the choke partly on.

Screwing this needle IN (clockwise) about 1/2 to 1 turn improves the problem somewhat, coming out of idle. Does not cure the problem. But the silly needle is so doggon' loose in the threads, I can't test it for long before it moves. It doesn't screw itself out; it screws itself more IN.

I will try the Teflon and report back. Thanks for the idea. It won't be for several days; I have long weekend plans.

 

[Dave.]

Drilled main jet from #77 to #76

Reviving this thread... The "long weekend plans" turned into a whole load of home projects while the mini bike sat in my parking space in the garage. I only got to work on it today because it's too bloomin' cold to paint windows.

So -finally- I was able to try drilling out the main jet. It was #77 and I drilled it out to #76. Before the drill, the engine was running on 1/2 choke, idling ok, but unevenly at high speed. After the drill, it still needs 1/2 choke to run well, but now it runs evenly at high speed. Still idling well, also.

Should I try drilling it out one more to #75 or just leave it alone now that it seems to run fine with 1/2 choke?

 

[chazdaddy]

Hello Dave,

Not sure what to tell you. I can't remember what I drilled my main jets to, mainly just drilled them out to next larger size. These carbs are not all the same anyway, what works for one is not the same for another, from my experience.

I can tell you I did drill out one too much and it did effect the way it ran. Probably ran better top end, but it would stumble a little at lower rpms then run great.

I have extreme fire danger on my property and I am very aware a spark from an engine could cause a fire. Recently I experimented with drilling out the muffler to install a spark arrester from 3.5hp Briggs. It worked out very well, has less back pressure, and engine seems to run a little better.

When I put the modified muffler on the engine with the main jet just a little too large, it cleared up the stumble. Probably my best engine now.

I would make sure nothing else is wrong with the carb. If it still won't run right without the choke on, it's not getting enough gas IMO. I would drill out the main jet to the next larger size. No guarantees, you just have to experiment.

 

[Dave.]

Thanks... I think I will run it for a while and check the plug to see how well it likes running 1/2 choked. As I said, drilled out one size larger, it runs smoothly now, both idling and high-speed, but still choked 1/2. So I'm thinking if the plug doesn't get fouled, maybe it's happy where it is.

You are in Dallas. Nasty weather there is coming this way. Was going to do a road trip for Thanksgiving (through the mtns), but I think that is a bad idea now.